10 minute read
Less is more
RIGHT AS RAIN
Although it’s one of the world’s most precious resources, with shortages all over the globe, water management is seriously lacking. According to the Global Water Partnership (GWP), 2021 saw record-breaking droughts, which are set to increase in frequency and severity. The Standardised Precipitation -Evapotranspiration Index (SPEI) Global Drought Monitor’s records indicated that in the US nearly half the mainland has been afflicted. Brazil experienced one of the worst ever recorded, and in Madagascar, drought has left hundreds of thousands of people malnourished.
As the planet’s temperature continues to rise droughts are becoming more severe across the globe. Is rainwater harvesting the solution to saving this scarce resource?
Rainwater harvesting is one solution that many countries have been investing in to tackle water shortages, but in the UK, where drought is less common or severe, this model is being used to reduce water consumption in an attempt to preserve our fresh water supply.
Rainwater harvesting (RWH) is the practice of diverting rainwater that falls on roofs or other surfaces of buildings, storing it and reusing it. This is something that is increasingly being used in the UK as a means to reduce our reliance on mains water, providing they are installed correctly.
“The UK doesn’t have enough water to meet growing demand, so using rainwater could be one way to reduce our use of public water supplies,” suggests Paul Millard, technical manager at Water Regs UK.
According to the Environment Agency: “If no action is taken between 2025 and 2050 around 3,435 million extra litres of water per day will be needed for public water supply to address future pressures.”
The UK public are on board, according to Water Regs UK, with nearly half of British people welcoming the introduction of RWH into their homes. However, tradespeople should be aware that installing a rainwater harvesting system is classed as a material change of use, so the local water company must be notified about the installation 10 days prior to work commencing.
“Systems can be directly or indirectly supplied,” explains Paul. “For a direct-supply system, water is pumped directly from the main storage tank, usually a buried tank, to the points of use, for example toilets and outside taps. Indirect systems are relatively similar to this in that they just add an extra step, pumping water from the main storage tank up to an intermediate cistern at high
DID YOU KNOW?
Rainwater harvesting systems typically reduce mains water use by around 50%
level, for example in the roof space, from where it can then be fed by gravity to the points of use. Some systems will treat the water to improve water quality.”
How it works
There are a number of different rainwater-harvesting systems available with a range of features. According to the Environment Agency’s Harvesting Rainwater for Domestic Uses information guide, BS 8515 gives guidance on the design, installation and maintenance of RWH systems for the supply of non-potable water in the UK, and applies to both retrofitting and new builds.
The code of practice covers three basic types of RWH systems:
• Water collected in storage tank(s) and pumped directly to points of use • Water collected in storage tank(s) and fed by gravity to points of use • Water collected in storage tank(s), pumped to an elevated cistern and fed by gravity to the points of use
With water collected in storage tank(s) and pumped directly to points of use, rainwater is collected and leaves and other large solids are prevented from entering the holding tank. The water enters the tank through a smoothing inlet, which stops sediment at the bottom of the tank from being disturbed by rainwater entering it.
A suction filter prevents the uptake of floating matter when the water is drawn up for use. As the water is non-potable, it travels through a separate set of pipes, as specified in the Water Supply (Water Fittings) Regulations 1998, and a pump pressurises the water.
The control unit monitors the water level in the tank. If the water level in the tank drops too low, the control unit will trigger an automatic changeover to mains water supply. The system must have a type AA air gap installed in order to prevent back-flow of rainwater into the mains.
When the water in the tank reaches a certain level, an overflow trap allows floating material to be skimmed off into the storm drain. A non-return valve needs to be fitted to prevent contamination of the tank by backflow, together with a rodent barrier.
Possible issues
Whilst rainwater harvesting systems have a significant role to play in reducing water consumption, it’s important that they are installed correctly to avoid drinking water contamination.
“Rainwater harvesting and water re-use systems need to be well designed, as well as being installed and maintained by those who are competent to do so,” says Paul. “It is critical that building owners and tenants understand the risks of incorrectly installed systems and ensure they only use suitably competent professionals to maintain their system.
“For reliability, a mains water back-up may be required and without appropriate backflow protection, will be cross-connected and risk contamination of the drinking water supply. That is why it’s so important that appropriate back-flow protection is installed as well as colour coding of pipework when carrying out work on the plumbing system. The colour coding should help to prevent anyone cross-connecting at a later date, as
Rainwater harvesting is an important part of sustainable building
45,193
litres is the average amount of rainwater a three-person household uses each year
67
baths is the equvalent water savings for a three-person household
20,336
litres is the volume of water saved using a rainwater harvesting system in a threeperson household each year
pipework could be mistaken for wholesome water supplies.
“British Standard BS 1710:2014 provides details on the appropriate identifi cation colour codes which should be used. It is also good practice at the point-of-use appliances such as toilet cisterns, outside taps, and washing machine connections to have labels indicating ‘Not drinking water’. This is essential particularly on outside taps so that visitors, such as friends, tradesmen and window cleaners, for example, understand the water is not wholesome mains water and can take the appropriate precautions when using it.”
Other issues with these systems may include traces of atmospheric and environmental pollutants and the water is likely to contain some animal and bird faecal matter. According to Water Regs UK, all alternative water supplies must be considered a fl uid category fi ve risk, that is to say they pose a serious health hazard. Other alternative water supplies from bore holes and rivers are likely to have a wider range of pathogenic organisms and possibly faecal matter and are placed in the same category. “Therefore, appropriate backfl ow protection for fl uid category fi ve should be installed,” insists Paul. “Collected rainwater can also become discoloured, smell and stain water fi ttings – particularly if it’s stored for longer periods and stagnates. That is why some systems will treat the water, but these will require greater maintenance.”
Upkeep
When it comes to maintaining rainwater-harvesting systems it’s vital to check the manufacturers’ recommendations. Thorough maintenance is important to ensure that end users achieve the maximum benefi t.
“A few simple frequent checks may be all that is needed for optimum system
Rainwater harvesting systems store water in a variety of di erent ways
A water abstraction licence may be needed if harvested rainwater is mixed with ground or surface water, which will be abstracted or transferred
Risky business?
Proper installation and regular checks should ensure water safety
According to the Rainwater Management Association, there are no recorded cases in the UK of legionella or other contagions arising from a RWH installation:
“Independent studies have shown the possibility of contagion to be very unlikely. It is recommended that the tanks used to store harvested rainwater are installed underground as they are large, and not particularly sightly. This means that the water is stored in cool and dark conditions which are not conducive to the cultivation of legionella. Where the harvested rainwater is to be stored above ground, protection from direct sunlight is recommended.”
Backfl ow prevention
The Water Supply (Water Fittings) Regulations 1999 require that su cient backfl ow prevention is provided to prevent contamination of the public mains water supply. This is usually in the form of an air gap that prevents non-potable water entering the mains water supply. Back-fl ow prevention for specifi c appliances should be discussed with the manufacturer to ensure suitable category fi ve (air gap) backfl ow prevention has been incorporated into the appliance. For more information on back-fl ow prevention and types of air gap, see the WRAS10 website.
According to DEFRA: “A Water Safe Approved plumber should complete regular checks on these systems to ensure the Water Fittings Regulations 1999 are being adhered to and any maintenance recommended by the system manufacturer should be followed.”
Systems must be clearly labelled
functions, as the manufacturer intended,” says Paul. “Users should be made aware of this and advised that it is in their interests to follow the manufacturer’s specifi ed maintenance requirements.
Installers should encourage end users to keep a record of what system has been installed and to share this information with the new homeowners if they sell the property or with any installer working on the plumbing or rainwater harvesting system.
“This is vital as rainwater harvesting systems can be altered and become non-compliant,” points out Paul. “One water company, which inspected over 1,000 rainwater harvesting systems over fi ve years, found around 70% failed to comply with the water fi ttings regulations, even though they had been inspected on installation and initially complied. Worryingly, a third of these failures were due to cross-connections, often put in to deal with faulty pumps or blocked fi lters – changes made post installation.”
Installers can help educate end users about the importance of keeping rainwater harvesting systems compliant with water regulations. The requirements of the Water Supply (Water Fittings) Regulations and Byelaws apply to properties that have alternative water supplies, such as rainwater-harvesting systems.
“The regulations and byelaws are intended to protect public health and make sure there is no waste, misuse, undue consumption, contamination or erroneous measurement of public mains water,” explains Paul. “Supporting the regulations, British Standards have published the standard BS EN 16941 Part 1:2018 for rainwater harvesting systems which covers their design, installation and maintenance. The document includes water quality requirements for the end users where the water is not required to be wholesome.”
Rainwater systems that treat water to higher standards to be used for washing or drinking would fall under the Private Water Supplies Regulations that deal with the use of abstracted water intended for human consumption, domestic purposes and food production. These basically follow the requirements set out for public drinking water standards and all rainwater harvesting intending to provide water for consumption or food production.
“Aside from what is required, it is also a good idea to make sure everything is properly recorded, pipes are marked and signs at taps and appliances are used so that any operator is fully aware of the quality of water being supplied,” advises Paul. “This will help users take the appropriate measures so that their
Feeling fl ush
Using rainwater in toilets dramatically reduces mains use
Toilet fl ushing uses the second highest percentage of water per person per day. Substituting mains supply for rainwater for this could potentially reduce pressure on mains supply by approximately 39 litres per person per day (l/p/d), or 26%, reducing the average daily use of mains water to 111l/p/d. If rainwater was also used to supply the washing machine and water to the garden, then the demand on mains water could be reduced further.
According to DEFRA: “A Water Safe Approved plumber should complete regular checks on these systems to ensure the Water Fittings Regulations 1999 are being adhered to and any maintenance recommended by the system manufacturer should be followed.”
family does not drink from taps supplied with impurifi ed rainwater. These actions not only benefi t the health and wellbeing of current users but of future occupiers, by raising awareness that an alternative water system has been installed.”
FIND OUT MORE
CIPHE members can order the Institute’s Rainwater Harvesting Guide for £16. Find the order form in the Membership Services section of www.ciphe.org.uk
