Rainwater harvesting and green roofs

Over here in the Freerain sales department we are regularly asked about mixing green roofs and rainwater harvesting systems. It seems that many clients and their designers/consultants throw as many of the eco-technologies together in order to obtain their ideal sustainable development.  We are obviously not suggesting for one moment that this is bad thing.  But it is important to recognise that often the practicalities of the function and use of the building has to come first.
So can you or should you look to incorporate both a green roof and a rainwater harvesting system?

Rainwater harvesting - the requirements

Firstly, it is important to stress the basic requirement for a rainwater harvesting system to function and deliver a good quality of water.  Virtually all experts in this field (our competitors!), agree that a clean, traditional and pitched roof produces water which can be simply filtered to remove general leaves and grit type debris.  Flat roofs can sometimes have areas which drain very poorly and have "semi-stagnant" pools which only flow under more intense rainfall.  After all a rainwater harvesting system can only deliver the expected quality of water, if it is supplied with it in the first place.  The rainwater system isn't going to increase the quality and of course, a poorly designed/sized system could adversely affect the water.

Why are green roofs specified in the first place?

Green roof technologies have emerged in the last decade or so and add value to the function of a building in a number of ways.  Firstly, planning in certain areas of the country see them as a way of blending into an area, for example if the development is within a green space.  Secondly, the roof off rates are much reduced, by the plants holding on to the water, before transpiring it back into the atmosphere.  This also means that the often the lightest of rainfall would never reach the ground or the surface water discharge system.  This is important, as attenuation design can be reduced.  Finally, adding there must also be some carbon reduction from the plants themselves.

So can you combine rainwater harvesting and green roofs?

Green roof technology is improving all the time, in terms of stability of the sub-structure, the membranes and the overall understanding of the maintenance requirements.  This all helps to keep the resulting water clean and in some cases probably cleaner than some traditional roofs.  So, technically you can, but we at Freerain, advises our customers that the choice is really an "either or" situation.  The main reason behind that, is not as above (water quality), it is actually a much more practical reason.  The amount of water available to a rainwater harvesting system is about 90% for pitched roofs and around 75% for flat roofs.  For green (or even brown roofs) the amount is 40% at best. 
So for example, a 100M2 London roof (pitched) might send 52M3 of water to the tank per year.  But if it was a green roof, this would fall to only 23.3M3. 

We also recommend additional filtration to remove the higher organic load.  Even with the use of fine filtration, our expectation is that the resulting water might still be slightly dis-coloured.  Obviously, adding more kit, adds to the overall cost of a system.

Verdict/Recommendation

At Freerain we recommended keeping green roofs and rainwater harvesting separate, this is because the amount of water available to the rainwater system is much lower, there is an increased risk of lower quality water and finally, greater costs are associated.  Therefore, a system costs more, has a bit more maintenance and produces less water. 

Hose pipe bans and British made underground tanks

So after two dry Winters, the UK is facing water restrictions, affecting areas from the South coast right up to parts of Yorkshire. The last similar ban was back in Summer of 2007, when the Southern water companies issues hose pipe bans.

Some fact!
Water companies in England and Wales leaked more than 3.3bn litres a day in 2010/11, according to the regulator Ofwat.
Demand for water stands at around 17bn litres a day, according to industry body Water UK.

It would seem that the UK climate has changed over the last 20 or 30 years, with more extreme weather, since 2007, there has been a number of high profile flooding events and the focus on the management of water had shifted from water supply to the control of surface water run-off. In reality both of these issues are never going away and should be tackled together. Short terms views on either will never solve the overall problem of water management in the UK. When the hose pipe bans were announced during early March, much of the media started talking about the need to create some sort of "national water grid" in other words move water from areas where it is plentiful to essentially the South and South East. This would potentially mean an awful lot of civil engineering, at quite an environmental (and carbon) cost. There doesn't seem to be a proper debate that includes rainwater harvesting.

Taking a more local approach would seem a better option, providing there is enough water available. Rainwater harvesting as many of you know has emerged during the last 12-15 years in the UK, brought over largely from Germany. Importing storage tanks from Germany has always been one of the main criticisms aimed at rainwater harvesting.

Freerain's parent The Gusto Group has tackled this very issue by investing in a rotational moulding factory and purpose rainwater harvesting designed tank moulds. The range of underground tanks include the following features:

1) 1800 litres up to 10,000 litres
2) Single piece, no need for messy on site assembly
3) Made from virgin high strength polyethylene.
4) Installed without the need for concrete back fill or bases
5) Supplied with telescopic access shaft and pedestrian cover.

www.gustotanks.co.uk

Freerain is obviously a customer of the Gusto Group storage tanks and have a number of different control systems built around them available. Garden rainwater harvesting systems are proving very popular at the moment, as customers look to store significant quantities of water for garden use and "beat the hose pipe ban" Find the garden rainwater harvesting systems here.
Garden rainwater harvesting can be a very good way to get involved with collecting rainwater, as trying to re-plumb a house to serve toilets and washing machines to an existing can prove difficult.

Remember you can use a rainwater harvesting system in the garden with a hose pipe, providing the water company imposing the restrictions haven't supplied the water.

Garden Rainwater harvesting

The Rain King 1000

With the onset of Summer and the news that we are facing water restrictions, not to mention brown grass! At Freerain Ltd we have been busy sending out one of our best selling products, The Rain King 1000. This is a basic, very DIY friendly due to the ease of the tank being hand-dig-able, but still a large enough volume to make a real difference compared to normal above ground water butts.
As part of the packaged the Rain King 1000, includes a 1,000 litre underground polyethylene storage tank, a downpipe filter and a stainless steel submersible pump. All this delivered on a pallet for only £869 (as June 2011). See garden rainwater harvesting for more information.

There are also storage tanks from 1800 right up to 10,000 litres with internal pre-tank filters for gardeners wanting even more water. These are also pumped systems and manufactured in the UK!!!

Above ground rainwater harvesting

We also appreciate that it is not always possible to bury a rainwater harvesting tank and so we also have a wall tank system, these are 800 litres each, so around 4 times the capacity of the traditional water butt and can be linked together to make really serious sized systems. Each system includes a tank, down pipe filter/diverter, a sight gauge and a pump. All the necessary inter-connecting pipes are included. See above ground rainwater harvesting for more information and current pricing.

We have received an so many enquiries from people who have been using water butts for a long time, and now realise that over the last few years, these are simply not large enough to last through significant periods of low rainfall. Also, when it is dry and hot, often this can be broken up by a heavy thunderstorm. We really need to intercept this and store it. Meaning that unless a decent amount of capacity is available, this opportunity will be lost.

Warmest April on record 2011

It has been reported this week that April 2011 (UK) was the warmest on record and figures out today shows that rainfall in most parts of UK were very low indeed. The south coast have received about 3-5% rainfall that they would have expected for April. Parts of Scotland were the exceptions with slightly above average, but only by a few percentage points.

The BBC are reporting that following a dry March as well, in terms of agriculture we could see food prices rise due to either lower yields and/or due to the cost associated with irrigation. This of course raise many questions, questions that are really beyond this post and indeed this blog.

We at Freerain have seen a massive increase in the number of potential customers looking for solutions to their water shortage issues. These range from the typical home gardener, who's traditional water butts ran out during the first weekend of April (if they lasted into April), to the small-holding needing a regular supply in larger quantities. We have also received enquiries from the leisure industry, for example pine lodge parks, these are often in slightly remote areas and need water mainly for irrigating their plants and in some cases washing down of the lodges themselves.

One question which is often aimed at rainwater harvesting is "if doesn't rain, what's the point of putting a tank in?" Which if you think about that, it is true. However, these dry spells (or actual drought conditions) are not rare events. Virtually every year we get similar stories in the news about lack of rainfall, coupled with increased demand (especially in the South East). Water shortages are not going away. So our customers are right to look to finding a solution not necessarily for their immediate problem, but for the next dry event.

In our office, we have been using rainwater harvesting to provide WC flushing and the occasional car washing function for about 12 years now and in that time we have seen many very dry spells. These are often combined with heavy storms in the middle of the hottest weather. These high rainfall events, fill the tank very quickly, which gives the office a supply for the next three weeks.

As mentioned above, garden watering is a hot topic (pardon the pun!) and it is much easier to install a system for gardening. This is because the is no requirement to change the household plumbing. Also, often the whole roof is not required meaning that the drainage also doesn't require substantial alterations. Our most popular systems are the Rain King garden systems. With the easiest of all and the most cost effective being the Rain King 1000.

For advice on garden rainwater harvesting and indeed full domestic systems, please visit our website Freerain or call 01636 894906 sales@freerain.co.uk

Water shortages again in the news

Well it's been the driest March for about 40 years for most parts of the UK. Already here we are in the 3rd week of April (2011 and there are stories in the news appearing about the water levels in our reservoirs.

The BBC has reported earlier this week that some of the reservoirs are currently at around 80% of the expected levels for this time of the year. But didn't we have a decent amount of rainfall over the winter (including the several bouts of snowfall)? So one dry month and the country seems to start running out of water.

Does this mean that we are in fact living beyond our means for water, especially with a drier climate predicted and an ever-increasing population?

This hightlights the need for a water strategy and one which embraces all available techniques, from water conservation right throught to localised capture/collection. Obviously we at Freerain are very focused on rainwater harvesting and we have seen from our own monitoring that a typical household can reduce their mains water demand by 50%. But also there is a need for education at various key levels to ensure that water is used carefully.

There has been some debate over the years surrounding the carbon cost of rainwater harvesting, but it must be stressed that a small amount of carbon is more than worthwhile to keep the taps flowing. Again, rainwater harvesting must be used together with various other techniques as part of an all round effort.

At Freerain we have recently launched a new range of UK manufactured rainwater harvesting tanks to further reduce the environmental impact of similar German imported tanks. These tanks can be used in domestic and smaller commercial applications. They start from 1,800 litres right through to 10,000 litres, all single piece and all have a very low profile. Being made from polyethylene and designed to be installed in very high water tables, they can be installed without concrete bases, backfills or surrounds. Domestic rainwater harvesting tanks

First a hose pipe ban and now canal issues

There is much talk in the industry regarding payback rates, carbon footprints and reliability issues with rainwater harvesting systems. Yet the real issue is the security of the national water supply. We have been far too relaxed over the last century, mainly thanks to the Victorian engineers, driven on by the industrial revolution. Also our perception that the UK climate is wet and therefore water is not a resource, it merely comes out of the tap anytime we turn it on. With an ever-increasing population, possible climate change, evidence is pointing towards more pressure on the most basic of resources.

In recent weeks we saw the start of the first water restrictions in the UK for four years and it was actually very surprising to see it not in the South East, but the North West. Whilst this is more of a pain than a real issue, it points to a potentially greater problem. A single dry season has been enough to stress the supply. Just this week we have seen further evidence of the environmental impact of an over-stressed water supply. As reported by the BBC there are closures of canal ways due to the lack of water, see here The Leeds-Liverpool canal is one of the major parts of the network. Not only does this imply the environmental concerns, but also the impact on tourism and the economic situation.

Also this week, people in the midlands are being asked to conserve water, to avoid a mandatory ban. See here, also from the BBC.

So when the issue of rainwater harvesting is being considered is simply not enough to consider it as a stand-alone solution for a single dwelling, project or even a larger site. Does it really matter that it might not payback in less than three years? Well certainly costs are important and nobody is suggesting otherwise, but maintaining supplies through the use of rainwater harvesting and other water conservation measures.

www.freerain.co.uk

UK Water Bills could rise

Background/Introduction

The most basic requirement in the UK, namely water is seriously under threat. Yet in this country we seem to be fairly blinkered into the carbon only argument in terms of our sustainable approach. Yes, carbon is a very important subject and measure of our environmental progress, but I would argue that it cannot and must be not used as the only measure.

With the UK's population set to increase by potentially 20 million more by 2050 and shifts in our climate (yet to be fully understood and determined), all resources will come under unprecedented stress. Added to this the current stress levels on water supplies in the South East of England, water conservation is a must.


Water of course is not only required for the most basic function, namely drinking, but it is fundamental to our crop growing and agricultural strategies. Recent studies have indicated that the availability of suitable growing conditions in the future maybe restricted to the wettest parts of the UK, i.e. Wales, Scotland and parts of the South West. Meaning that the traditional cereal regions, such as East Anglia and Lincolnshire would be lost from production. Yet more resource stress.



Planning



Strategic level planning for water is centered on the extra people and the dwindling (expected) rainfall predictions. So less water for more people. Currently in the UK we "enjoy" an average of 150 litres per person per day, more in certain areas of the country, the South East. The Code for Sustainable Homes (CSH) aims for a reduction to 80 litres per person per day at code level 5 and 6. For many this would be a complete change to their way of life. Potentially ending "taken-for-granted" activities, such as a full bath or nightly garden watering etc.



Rainwater harvesting - a solution



In the UK we have been fairly slow to adopt rainwater harvesting, this in part is due to the lack of financial incentives. In Germany, where rainwater harvesting is widely used, the cost of water is significantly higher than here in the UK. Lack of grants for rainwater harvesting, such as those enjoyed by other technologies, such as Solar, has made it difficult for business and individuals to justify the expense on paybacks alone.
Better technology, the recently published BS8515:2009, improved supply chains, installers and understanding will help to reduce the overall cost of installing a rainwater collection system.

However, a warning from the water companies suggests that the cost of water is moving up and one report recently in the Daily Mail suggests 27% above inflation.

http://www.dailymail.co.uk/news/article-1267821/Water-bills-soar-industry-unsustainable-firm-warns.html

Rivers may run dry

Recent press reports have again highlighted the pressures on national water-supplies and the consequences if steps are not taken now to reduce consumption.

All the main national newspapers have now carried articles outlining the likely effect on national rivers if water continues to be extracted at current rates; within a relatively short number of years substantially reduced summer flow-rates are predicted.

Alongside this scenario, the press have also been reporting that the fitting of water meters is to become mandatory. Water meters are shown to play a useful role in reducing mains water consumption, although some claim that this can have a unfair impact on the poor.

So far, articles such as the above have failed to draw the link between reducing national mains water consumption, and the widespread introduction of rainwater harvesting, which reduce domestic consumption by around 50% without any adverse social and environmental effects.

Use for commercial and industrial applications, this mains water saving can rise to in excess of 80% on any building that combines a large roof, with a high demand for non-potable for applications such as toilet flushing, clothes washing and outside use.

Rainwater harvesting tanks: Do they need cleaning?

Introduction

Rainwater harvesting systems are becoming increasingly popular, and the fact the Freerain's early customers have had their tanks installed since 1999. Many people are considering the long term effects and issues concerning older rainwater harvesting systems.

Cleaning?

The general water quality and effectiveness of a rainwater harvesting system is largely dependent on the size of the storage tank installed. Too large and it may never overflow and turn the water over enough. Too small and it doesn't store enough water to be effective and the dwelling/project is reliant on mains water top-up.

Assuming the storage tank has been sized correctly, then it should overflow a few times a year, assuming the system includes a calming inlet and has a suitable pre-tank filter, then the tanks really shouldn't need cleaning. The heavier particles should be removed by the leaf and grit pre-tank filter, the finest particles should float and be skimmed off during overflow. The particles in suspension eventually get sucked up by the submersible pump and are then removed by the inline strainer/carbon filter or whatever has been included on the system.

So a well designed system is very unlikely to need cleaning out, but there is one big assumption, this assumes that only roof water has been sent to the system. Water from hard-standing should not be sent to the rainwater tank, nor should water from a green roof system. Although newer green roof systems do filter the water very well. The overflow from the storage tank should also be protected from backing up. In other words, a well designed system, being used in a normal way, should NEVER need cleaning.

Germany

In Germany rainwater harvesting is about twenty years ahead of the UK and their experience is exactly as described above. Only poorly designed or mis-used systems require major maintenance.

Roof top rainwater storage, does it work?

If you think of a traditional rainwater harvesting system, in the UK and most of Europe. Then you would probably think of an underground storage tank, a physical filter before storage and a pumping system. We have previously looked at the options for controls and this is broadly two types. The direct pressure system and the header tank system, being fed from the underground tank.

We at Freerain Ltd, are asked quite often about the option of eliminating the underground storage tank and diverting roof water directly into a header tank. On first thought this seems like a good idea, no excavation, no underground tank and maybe even no pump!! All sounds pretty good?

Domestic system, we need storage of around 800-1,000 litres per person to make the rainwater harvesting system effective. So a 4,700 litre system when full would weight around 5 MT!! and take up a considerable amount of space. In order to strengthen the floor, it could be very costly and indeed more than a non-concrete underground tank installation. (as per Freerain tanks). We have also previously discussed the fact that the water should remain dark, cold and not subjected to thermo-cycling (that is rapid heating and cooling). Whereas inside a building it might be. Finally, the overflow from storage would need to be designed to never flood the building at times of heavy rainfall.

Commercial systems are more likely to be specifically designed to take the weight, if underground or above ground outside is not possible. But internal sectional storage tanks do tend to me more expensive and take up valuable space.

Filtering the water prior to the storage tank can sometimes be problematic. A traditional underground system utilises gravity to move the water from the roof, through/across a filter and finally in to a storage tank. The rainwater filter is normally either housed in the tank neck (as with Freerain domestic tanks) or externally for larger commercial systems. So if you want to have a high-level storage tank it must be designed to be able to accommodate any invert drops across the filters and the overflow.

In summary, for domestic projects we wouldn't consider it as a viable option, too much weight or too small amount of water stored. For commercial projects it is always an option, but only if underground or above ground external has been considered and rejected first.

Rainwater harvesting and water restrictions

Question: I've got my rainwater harvesting system installed, should I worry about hosepipe bans and other water restrictions?





Answer: You need to be aware that most rainwater harvesting systems are in fact ultimately connected to the mains water supply. Therefore, you can use water from a hose, providing the local water company (imposing/enforcing, the restriction) haven't supplied the water.


We at Freerain, routinely supply systems without a mains top-up specially for external/garden rainwater harvesting This ultimately protects the customer from any grey areas or mis-understandings. Quite simply, if the hose/sprinkler has water, its rainwater, if not the tank is empty!!!

For the latest information about hosepipe bans and general water restrictions, I would recommend visiting Hosepipeban.org.uk There you will find links to the water authority sites, water saving tips and a forum.

We may not have had any major water restrictions in the UK for a few years, but with a population increase and the effects of climate change, we are certain to have more water stress.

Another solution

Where rainwater harvesting systems are used for both internal and external demands, a mains top-up is essential. Direct pressure systems (whereby the water is supplied a pump pressure) mains water must pass through a class AA air-gap (see WRAS) to avoid any cross-contamination between potable and non-potable water. The easiest way is to top-up the external (underground) storage tank with mains water at time of low level. This then raises the possibility of a hosepipe supplying mains water on to the garden. Which during a hosepipe ban would make the system fall under the ban. One water to remove this is to install a header tank (break tank) in the property. This way, pump pressure can be sent to the outside tap directly. But all the mains water topping up occurs in the the header tank. So, the only water to pass through a hosepipe would be the locally collected rainwater.

Is Legionella problem for rainwater harvesting systems?

Introduction

Legionnaires' disease, or Legionellosis is an infectious disease caused by a genus of bacteria. These bacteria thrive in warm conditions typically between 25-45oC. There are several types of Legionellosis, but for the point of this blog we are only going to cover the most common type. The condition is much like severe pneumonia and can be fatal. The first and still the most famous outbreak was in 1976 in Philadelphia, where it was given the name Legionaries disease. A gathering a war veterans were together for an annual event, see here. In the UK cases are rare, mainly due to the strict regulations now in place, but in 2002 there was a case where 7 people died and about 170 contracted the condition from a nearby cooling tower.

It is estimated that around 10,000 people die from the condition per year in the USA.


Legionella bacteria: Conditions for growth


The bacteria thrives in a range of temperatures between 25-45oC, but does indeed survive at lower temperature, but is dormant at around 20oC. As with most bacteria it requires a moist, if not aqueous environment. So the focus for the regulations has been centered around hot water systems, such as showers, heating and hot tubes. But also ventilation systems, whereby water is used as the indirect heat source.


Pathway and transmission


Infections normally occur through the respiration system in the form of fine spray (aerosols) and so it not the water body itself. Therefore spraying, minor leaks in ventilation systems and bathing or the areas of special concern.


Rainwater harvesting systems, are they a potential risk?


A well designed rainwater harvesting system is designed with the quality of water in mind and this is usually dominated by the tank size. Sizing the storage correctly ensures that the water is not stored for too long (around 20 days) , but balancing the need to supply water. Generally speaking in the UK, we don't have very long dry periods, but you might be surprised to learn that on average we receive significant rainfall about every two and half weeks. Therefore, storing very small quantities (relative to demand) is not efficient and in many ways pointless.

In the UK the rainwater tanks are normally underground and include a pre-tank filter. This helps in several ways. Firstly, being underground the temperature is no more than about 10oC even during mid-summer. Secondly, the pre-tank filter removes much of the organic matter and this prevents the build-up of bacteria generally. It is also dark. So the water is kept cold and dark and in many respects clean. Many systems use calming inlets to the tanks. This helps to retain higher than normal oxygen levels, promoting healthly aerobic bacteria. See the Environment Agency for more water quality discussions.

In certain commercial applications such as schools, we at Freerain advise the use of ultra-violet sterilisation unit. Whilst it is not part of any regulations, we feel that it is a belt and braces approach to rainwater harvesting. Especially where the project utilises a header tank type system. That is a secondary storage tank at high level. This is because of the usage pattern of a school year. There could be several weeks during the year, where water could be sat in the header tank. We are not saying that there is any risk of legionella at all, but many consultants and specifiers are not prepared to include a system without a UV unit.

Another application for adding a ultra-violet unit is for irrigation systems, where there is the chance that rainwater could be sprayed as an aerosol. Also, the water is often kept longer as water quality is less important. Finally, some are above ground tanks. Adding the ultra-violet unit again is not part of regulations, but it is a cheap option, sometimes costing as little as £400.


Summary


Rainwater harvesting systems are not a source for legionella bacteria to thrive, due to the conditions the water is kept. That is much colder than the lower limit for growth as researched by the Reliance Worldwide organisation. The water is generally clean before it enters storage and used quickly before it deteriorates.
The focus is quite rightly on hot water systems and not cold rainwater systems. Care should be taken, but a well designed system from a well respected supplier/designer remains important.

East Midlands EXPO 19th November 2008

Freerain Ltd is attending the East Midlands EXPO event at the Lincolnshire Showground's Epic Centre. The venue was chosen due to its environmental and sustainable creditials.

The event is free to enter and open to the general public to gain an insight in to the latest environmental trends and products and also attend the many seminars delivered by a number of professionals.

The centre, sometimes known as the Epic Project was a purpose built exhibition centre with a whole host of sustainable technologies. Indeed Freerain supplied the rainwater harvesting system and this was installed by local contractor Sleaford Building Services (SBS Ltd). Other technologies included wind turbines, biomass heating, solar and PV. Along side the technologies were traditional construction methods, including the use of natural ventilation, minimal use of steel and concrete. With a general focus on a sustainable approach to construction.

The rainwater harvesting system supplied was:

18,000L GRP underground storage tank
VF2 Filter roof filter
Duo-204 control system (two submersible pumps)
Expansion Vessel
UV Filter

Rainwater Harvesting: Oak Tree House

Oak Tree House in Knaphill, Woking is a three bedroom detached house that has been refurbished as a show house, for local people to gain an insight in to how they might reduce their own domestic energy and water usage.

The project was completed by energy partner ECSC, building partner Mansell PLC and Environmental partner, Woking LA21, Woking Borough Council in November 2008.

The project covered several aspects of sustainable living and these included:

Sustainably sourced furnishings
High level of insulation
High-efficiency boiler and heating controls
Solar thermal hot water
Solar PV
Passive solar harnessing
Rainwater harvesting
Water conservation measure, such as aerated shower and aerated taps.
Drought resistant plant species in the garden

Freerain Ltd, supplied a 3,500 litre rainwater harvesting system to the project.
The system which retails at around £2,200 + VAT (supplied only) includes a tank, submersible pump and a control package. This system also draws mains water when there is insufficient rainfall automatically. Therefore the homeowner doesn't have to do anything, but a simple filter clean about four times per year. Should the house receive average rainfall for the area, the system could provide up to 70M3 of water during the year. This means that the water use for the house with an average family will broadly halve.
The collected water is non-potable, which is suitable for WC flushing, washing machines and all outside tap functions. Along with permeable paving, the rainwater tank will help to prevent localised flooding issues, that are often associated with urban areas.

The house will be shortly open to public as a demonstration property.

Ultra-violet sterilisation as an upgrade for a rainwater harvesting system

Background

A rainwater harvesting system (sometimes wrongly called a grey water system) can be defined as a system which collects roof water for use as non-potable water. Much is written on the Internet and talked about with rainwater harvesting (recycling) systems about the use of ultra-violet sterilisation as a means of sterilising the water. Typically a rainwater harvesting system will have a physical "leaf and grit" type filter or filters. This is perfectly good enough to clean the water for uses such as WC flushing (accounts for 25% of daily water consumption), washing machines and outside taps. It is possible to upgrade the water to fully drinking (potable) standard. A good upgrade should also include a fine filter prior to the UV unit. The filter needs to be reducing particles smaller than 5 microns. This is because of the "shadowing" effect. This means that should the particles be greater than this, then bacteria and pathogens can be shielded from the UV light source. This finer filtration is often in the form of carbon filtering, and usually in sealed purpose made cartridges.

Potable upgrade or not?

So, it is possible to upgrade the collected water from a rainwater harvesting system, but is it actually worth it? From the paragraph above, you can extra equipment is needed to the rainwater recycling system. This can cost from around eight hundred pounds. With consumble carbon cartridges and a mains power operated ultra violet sterilisation unit, these have a running cost of around two hundred pounds per annum. Which in some circumstances is perfectly reasonable. For example, if a dwelling is off-grid by the remoteness of the site, then a private water supply is very desirable and a running cost like this is very affordable. But where mains water is freely available, and the householder is looking for savings or to be more environmentally responsible, then perhaps this type of upgrade is not worthwhile. As the manufacture of the UV bulbs, equipment and carbon filters contributes to industrial environmental damage. The extra power to use the system and the fact that mains water is already available, makes for a strong environmental case against upgrade, but using a rainwater harvesting system to supplement mains water and in most cases halve the amount used is a much more compelling case.

Quick calculation

Let's take a 150M2 roof in Surrey, 3 bedroom house with 4 people living in it.
The property might collect around 95M3 of water per year. The demand that could be fufilled by rainwater would be around 66M3 per year. If this project was to be upgraded to fully potable (drinking) standard, then the property would be using around 132M3. So, in this case there wouldn't be enough water to meet the demand. So, depending on which type of rainwater recycling system was installed mains water might be re-treated. This is because a direct pressure system tops up the external storage tank with mains water at times of low rainfall (or high demand). Making the idea of installing the potable upgrade not worthwhile.

Commercial rainwater harvesting system

Many commercial specifications include UV sterilisation units, this is not due regulations, but more because the client "decides" it's the thing to do. Often encouraged by industry professionals, using their experience of hot water systems. Legionnaires' disease is often mentioned, but this is only a problem where the water is held at temperatures over 25 oC. Rainwater stored underground is very unlikely to ever reach those levels. So it's not a problem, but in a £30M project a few hundred pounds is a very easy belt and braces approach for specifiers.

Rainwater recycling: Types of control systems

Background and introduction

Rainwater recycling or rainwater harvesting as it is more commonly known is a fairly well mature technology that was developed during the last thirty years. Essentially the storage and filters quite simple. But the control systems are more complex driven by the need for reliability. In the UK, we have mostly thanks the Victorians enjoyed a safe and reliable water supply for the last hundred years or so. It's really in the last fifteen years where terms such as water stress has started to be used. The Environment Agency suggests that everywhere south of the Humber estuary is under some form water stress and of course the drier south and south east is continuing to see an increasing population.

Types of controls

There are three main catagories of controls with most rainwater harvesting systems.

1. Direct pressure systems
2. Header/break tank systems
3. External use only (Gardening) systems

Direct pressure

Direct pressure systems work by supplying water at pump pressure directly to the point of use via a control panel. This panel also controls the mains water back-up arrangements, of which there are a number of different configurations between different manufacturers. But all systems must comply with WRAS regulations and this put simply here is concerned with an air gap (type AA) to eliminate direct contact between potable and non-potable water. There are also regulations regarding pipework identification.

These systems are normally installed in lower demand situations such as domestic single dwellings. Where the demand is much higher, more than one pump can be used as duty standby assist type arrangements.

Header/break tank

These systems differ slightly from the direct pressure systems as the main pump or pumps send the water to a header tank (gravity system) or to a plant room based break tank. Where required additional pumps are used to boost the water supply around the building. These types of systems tend to be used in more commercial/industrial projects. Similar water regulations also apply to these systems and a slot/ cut-away (AB type airgap) is also required.

Garden rainwater harvesting

These systems were developed in response to the hose-pipe ban/water restrictions that were in place arouns 2006 (UK). They tend to have a lower specification generally, and most importantly the mains water top-up arrangements are usually excluded to protect the end user from falling foul of the water restrictions.

At Freerain Ltd, we have developed numerous various on the themes above to suit the project requirements and indeed are contuning to develop new ways to improve the performance and interface with BMS systems and other systems. More information about commercial rainwater harvesting system can be found on our website.

Rainwater harvesting: Millennium Green case study

Gusto Construction Ltd, completed a development site of 24 houses in 1999. Each property on the Millennium Green site was built to a standard far beyond the building regulations and achieved the status of Eco-Excellent. Each property was fitted with a Freerain rainwater harvesting system to meet the water reduction targets. Most of the plots were fitted with a 3,500 litre or a 4,700 litre storage tank, depending on the size of the plot. The system uses a submersible pump to deliver the stored rainwater directly in to the property, without the need for a header tank. The resulting water is suitable for WC flusing, washing machines and outside tap functions. The water is not suitable for drinking or bathing, as this water is non-potable (sometimes called reclaimed or even greywater).

During the year 2001, the Environment Agency and Severn Trent Water carried out a study on one of the plots at Millennium Green to see the progress of the rainwater harvesting system (sometimes called rainwater recycling). They looked at various aspects, including reliability, water quality and amount of mains water was displaced. The weather pattern for the year was not unusal and certainly could be considered an average year.



The above image (available on the main title link in a larger form) shows the level of water in the storage tank day by day. This showed that on a few ocasions a few litres of mains water was added to the storage tank. This is very beneficial as mains water has certain chemicals in it, and the free chlorine does help to maintain the freshness of the water.

Also several times during the year the tank overflowed, which a well designed rainwater harvesting system should do. This allows for any scum layer and suspended particles to be washed. With the Freerain system, the pre-tank filter is housed in the neck of the tank, this allows for the overflowing water to back-wash the filter. Thus reducing maintenance and maintaining water quality.


The study also monitored the amount of water used in the property and the above figure shows the daily percentage split between mains water (in blue) and the rainwater (in grey). The split was almost 50% of each. So when considering the Code for Sustainable Homes you can see that a reduction in mainswater consumption of 50% would mean that per person per day the average usage would drop from 150 litres to 75 litres. An article written on behalf on the Good Homes Alliance suggests that the resulting homeowners might no wish to purchase houses that have the perception of lowering living standards, with water saving device and smaller baths. But the Gusto experience shows that with a typical house and a typical family using water quite freely, a rainwater harvesting system can meet very high standards. All this without comprimising on the lifestyle.

Brief history for Freerain and the Gusto Group.

Gusto Construction is an award winning private developer based in the East Midlands of England. Gusto Construction has built various environmentally friendly housing developments, whereby the houses are rated eco-excellent and some of these were built as long ago as 1999, when this standard of build was truely pioneering. With such a small market for environmental building products back then, the supply chain for the technologies was also difficult.

The most difficult was a rainwater harvesting system or a rainwater recycling system as it was known as. Freerain Ltd (formerally known as Gusto Products) was formed to meet the initial requirements of Gusto Construction Ltd. With other areas of the Gusto also forming, the Gusto Group of companies has been operating since around 2003.

Freerain Ltd was also a founder member of the UK rainwater harvesting association, which was formed to tackle the issue of standards and compliance within the industry.

Freerain initially began supplying Gusto Construction for its Millennium Green Development, but the high quality and ease of installation systems soon attracted attention from other developers and self-builders. Freerain quickly established itself as one of the market leaders in the UK.

Following on from several water saving related awards, larger projects began to consider rainwater harvesting. Commercial rainwater harvesting systems come in all shapes and sizes and with that we bespoke the design as necessary.

Types of rainwater harvesting systems

Introduction



The term rainwater harvesting is used to mean the collection of roof water (typically) from a building to provide that building with water to displace mains water. Rainwater in its untreated form can be used instead of mainswater (potable). This means that you can use rainwater (non-potable) in WC's, washing machines and all outside tap functions. Our studies have shown that this accounts for approximately 50% of all water used. So from an environmental perspective, we reduce our mains water consumption by 50%. (subject to the amount collectable from the roof). In commercial projects the amount could be much higher. As the vast majority of water used in an office is for WC's.

Rainwater harvesting systems are have a essentially three main components, these being:

• Storage tanks


• Filters


• Control systems

But there are of course variations on the above.

1. Storage tanks, these can be underground, above ground single peice, above ground sectional. Made from GRP, concrete, plastic or metal.


2. Filters, course leaf and grit, self-cleaning, backwash and inline strainers.


3. Controls can either be direct pump pressure, header tank (gravity) with or without mains top-up. They have a single pump or multiple pumps. These pump can either be submersible (in the tank) or suction pumps (sited with the control panels).
   

In addition to the main components, all items are sometimes added such as ultra-violet sterilisation or monitoring panels as shown above. These add-ons are not required in order for a system to function, but they make the systems more pleasant work with.

When using a rainwater harvesting system it is important to ensure that it complies with the water regulations (WRAS). This is mainly concerned with the cross-contamination of potable and non-potable water and also correct pipe markings inside and outside the building.

Rainwater harvesting Case Study: National Centre for Autism Education

Freerain has recently supplied a rainwater havesting system for installation by Working Environments Ltd (Mechanical & Electrical contractor). The National Centre Centre for Autism Education has been built for the Treehouse Trust.

Source: Treehouse Trust Website, accessed 15 Oct 2008.

Sustainability
The building has been designed to be a low energy and low carbon building. The building is predicted to use 67% less energy than the energy benchmarks set out in the Greater London Authority's guidance for planners. 10% of the energy will be derived from renewable energy sources (ground coupled air pipes).

TreeHouse’s ‘Green Features’ include:

• 
  The roof will be planted with environmentally friendly sedum, creating a habitat for native flora and fauna; softening the visual impact of the building; and providing insulation to reduce the need for additional heating.
• 
  Rooflights on the first floor will ensure maximum daylight levels. Light shafts will provide daylight from the roof down to the ground floor classrooms to minimise the amount of artificial light needed.
• 
  Artificial lighting will be controlled by photocells linked to dimmers to minimise the artificial lighting load.
• 
  Energy efficient boilers will minimise the gas load for heating and hot water. The efficient fabric, form and air tightness of the building means that the heating load is low.
• 
  Rainwater recycling system will supply the WC flushes, reducing energy used in treating and supplying water to the building and treating surface water drained from the building.
• 
  High performance glazing will minimise solar transmission in summer and heat loss in winter, while still maintaining high light transmission to retain daylight levels.
• 
  A ground coupled air system will use the thermal mass of the ground as a heat source in winter (warming the incoming air) and as a heatsink in summer to cool the incoming air. This will result in a carbon saving of 10% or 1056kg/year.

The rainwater system supplied by Freerain included:

• 51,000L underground storage tank (including 27,000L of attenuation volume)
• 4no. Hydro-filters, these are a relatively new type of filter, originally designed for metal reduction from road run-off pollutants.
• Header tank type control system
• Ultra-violet sterilisation system
• Various pumping controls
• LED rainwater monitoring panel

The combination storage tank has allowed the surface water discharge to be controlled, but also cost savings on the total installation.