... introduction to rainwater harvesting...

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2 ... introduction to rainwater harvesting... water-supplies under stress... Pressures on water supplies and the need to man- mains water supplies. age surface water run-off are placing twin pres- Conversely, and just as important, Planning Regusures on designers and developers to address walations have required for some time that on most ter-related issues from the outset of any new prosites the surface-water run-off must be attenuject. ated, or in some other way controlled, to restrict run-off to the pre-development level, or at some With the average rainfall per head in the south of other specified rate. England less than around the Mediterranean, and the population continuing to grow, water supplies cast-qfictive & holistie soluaion... in all the English regions south of the Humber are already stressed, in most cases at a critical level. Rainwater harvesting is internationally recognised cost-effective solution to both water-supply meeting building codes... and site water management issues, able to provide a fully integrated and flexible response to This is reflected in the Code for Sustainable site specific requirements, including providing Homes, and commercial equivalents such certainty of supply for emergency uses such as BREEAM assessments which require that all new fire-fighting. buildings are designed to reduce the demand on

3 the harvesting process basic principks,,. The basic principle of rainwater harvesting is sim- from the drain pipes to a storage tank, via a filter. ply to capture non-potable rainwater (non- drinking standard) at the point of fall, then substi- The storage tank can be above ground^ but for tute it for mains water for applications such as: Toilet flushing Clothes washing machines Garden irrigation Car and fleet washing Forecourt and plaza wash-down the best water quality underground storage is to be preferred. Once stored, a suitable control sys- tem is then used to supply the water to the de- sired services using a durable electric pump. water available... Conversely, untreated rainwater is not suitable The amount of water available for collection defor use where drinking quality water is required, pends upon local average rainfall, roof size, such bathing, showering and dish washing. drainage efficiency, and the efficiency of the filter how it works... being used. Multiplying the roof area in metres, by average The harvesting process is very straightforward, rainfall in millimetres, and by the roof and filter involving no more than channelling the water efficiency factors gives annual yield in litres.

4 sizing the system......fo r the home and the workphce... The amount of non-potable water likely to be a household's non-potable water requirements; used depends upon factors such as the occupancy this in turn amounts to around half of total water of the building, be it a home or the workplace, consumption which means that mains water con - the purposes for which the water will be used, sumption is reduced by around 50%. and the efficiency of the appliances (such as toi- lets and clothes washing being fed. In the workplace, or at leisure facilities, the balance of the water being used often switches to - Because rainfall does not fall every day, the stor- wards non-~otable such as toilet age tank must be correctly sized to reflect two flushing, grounds irrigation or fleet washing which competing factors, namely,quality of water and means the potential to reduce the consumption continuity of supply. In practice this results in a Of mains water isgreater. tank that provides around days demand without any fresh rainfall This potential can be realised if the building also has a good capacity to collect rainwater (ie a large mains water savings... roof), with mains water savings of more than 80% being easily realised in any building that combines The operational performance of properly de- a large roof with a high demand for non-potable signed systems is sufficient to provide nearly all of

5 ... keeping it ckan & safe rainwater harvesting is the answer., I water quality... additional purification... The quality of harvested rainwater depends upon Where a specific requirement exists, for example good design, high quality components and good where a building cannot access the national water installation. Water quality can therefore be com- grid, harvested rainwater can be brought up to promised if any of these are absent. Water falling from the sky is usually clean, and potable (drinking) water standard by inclusion in the system of additional purification devices. only becomes compromised when it reaches the Generally, however, this is neither a necessary or ground. Provided, however, it is then harvested recommended practice due to the added costs in accordance with UK-RHA recommendations incurred. and the relevant British Standard (BS 8515) it remains safe to use for non-potable purposes. code of practice...?commended use... For additional peace of mind, all UK-RHA mem- bers operate to a strict Code of Practice designed I The recommended usage of harvested rainwater to ensure that users' requirements predominate; in the UK is therefore restricted to toilet flushing, system conformity with the national standard for clothes washing machines and outside use as rainwater harvesting (858515) is also required. listed earlier. I

6 range of options the best system for you... full domestic systems... : Rainwater harvesting systems come in many Full domestic systems are best installed whilst a guises, the most basic being a simple water butt property is being built or refurbished, as separate which offers a very limited supply of water of in- pipework is required to the non-potable services different quality. to be supplied ardening systems... Domestic systems also incorporate mains water top-up facilities to ensure continuity of supply For keen gardeners, undergound systems offer during prolonged dryspells. the twin advantages of providing a water supply capable of lasting through a long hot summer, comme~cia/-sc~/e~~ms whilst minimising the aesthetic impact of a large above ground tank.,.. Commercial systems are also best installed at the new-build stage, although they can often be Such systems are straightforward to install to any retro-fitted if the sewice runs/ducts are readily existing building and, provided they are not accessible. A wide range of tanks sizes are avail- topped-up from the mains, are not subject to able to match the high harvesting potential of hosepipe bans or other water restrictions many commercial buildings.

7 'c-,-flp:, ;? b, 8 > \'..,?.I 5u&&.i*... the keys to getting it right... reliable & expert suppliers... best practice... is the answer... All UK-RHA members are experts in their field, be Best practice is to collect rainwater from hard St as component suppliers, or as designers, manu- roof areas, and filter it before storing under- facturers and suppliers of full systems. Involve them from the out- set of your project for peace of mind and the most cost-effective solution skilled installers... Systems should always be installed strictly in accor- ground. Water from other hard-standing areas such as car parks can also be introduced into the system subject to suitable filtration to remove hydro- carbons and other impuri- ties before storing. And legal... Systems must: tions Meet Water Regula- dance with the manufacturer's instructions, by. Be separated from any mains back-up by tradesmen who are accredited for the installation type AA or type AB air gaps of rainwater harvesting systems. Have pipes and taps properly marked Have lockable lids on underground tanks.

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