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.

Suitability of rainwater harvesting systems for existing dwellings

Domestic rainwater harvesting systems are generally aimed at new-build.
There are several reasons for this and these are:-

• The drainage can be designed specifically with the rainwater system in mind.
• The way the internal plumbing is arranged differs slightly to separate out the potable and non-potable pipe work
• It is often easier to move the tank around the site before the building is completed.
• Excavation machinery is already available.

The costs associated with installing a system are reduced by the above factors, making them more affordable.

When considering an existing property is can be very much more expensive, starting with the fact that VAT is added to the system price. This is currently 15% (recently 17.5%). But moreover, re-routing pipe work can be very expensive and can involved fairly major cosmetic works. The external drainage is often difficult to access, either due to hidden pipe runs, unworkable invert depths and/or unknown modifications.

It can also be difficult to get the tank to the desirable location around the property. For example a semi-detached house, has only access around one side. Often this is limited. So a crane cost must be added to the project.

Space in the garden can also be an issue, as digging close to foundations can be risky and require a professionally appointed structural engineer to advise on the works.

So, with the extra costs and the fact that water is actually still relatively cheap in the UK, there isn't the financial incentive to harvested the rainwater.

At Freerain, we advise customers with existing properties to consider a system for external/gardening use. This is because the internal plumbing is changed and perhaps not all of the drainage is needed to be centralised. This reduces the costs significantly, but of course not everyone is satisfied with external water only.

For commercial projects, these are reviewed on an individual basis, this is because the very nature of some of of the sites. External drainage can sometimes be very easily accessed, above ground tanks are more acceptable and work technically better.

In summary, rainwater harvesting systems are best suited to new-build projects for domestic dwellings, but perhaps commercial sites can with certain modifications incorporate a system.

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.

British Chamber Awards 2008

Freerain took a party of four to the British Chamber Awards 2008 dinner hosted by Sian Jones and Dermot Murnaghan.

The awards were held in the fantastic venue, the Natural History Museum. There were approximately 550 people from all over the country from sole traders to multi-national comapanies.

Freerain were nominated in the Green Business category having previously won the regional round a few months previously. There were in total seven companies in total representing the Nottinghamshire and Derbyshire chamber this year, across the various different categories.

Unfortunately, we didn't win the award, but it was a great pleasure to be nominated and clearly shows how the hard work by all the staff is really paying off.

The green award was one of the most competitive of all of the awards and this clearly demonstrates industries comittment to environmental issues.