Keeping it clean: with rainwater

Despite the summer’s excessive rainfall, many parts of England south of the Humber suffer from various degrees of water-supply stress. This, coupled with cost issues gives fleet managers another good reason to review their current lorry-wash arrangements, says Chris williams

With a typical distribution hub likely to have several acres of roof-covering and lorry hard-standings, rainfall has traditionally posed more of a problem than a benefit. Modern building regulations increasingly demand that no more water must leave a site via the local storm-drain system following development than did when it was a green field.  In practice this means that land must be put aside for drainage “swales” or underground water-attenuation systems installed.

As we all know, every problem presents a new opportunity. In this case this water can be put to a productive use with minimum effort and cost. By using simple and reliable automatic rainwater harvesting techniques the rainwater can be used for fleet washing purposes.

Recently a major regional distribution centre for a high street retailer, made a very substantial investment in attenuating the water running-off 4-acres of roof. In addition, subsequent investment was necessary to ensure the delivery of sufficient mains-water to the site to satisfy fleet-washing requirements. Surely, at some stage someone might/should have considered the financial and environmental advantages that would have arisen from using the harvested rainwater, already being collected for attenuation reasons? The water collected could have been utilised for fleet-washing, toilet-flushing and grounds-maintenance purposes.

Hopefully, recent media publicity will now help to bring to the mind of every commercial designer and specifier the need to fully take into account the environmental and financial benefits of using harvested rainwater to satisfy a development’s non-potable water requirements.

Water on demand
Capturing rainwater for subsequent re-use is simplicity itself, with the same principles applying to both domestic and commercial applications.  Instead of being directly channelled to soak-aways or storm-drains the water falling on the roof is simply fed into a suitably-sized storage tank. Here it is kept in good condition by filtering-out solid matter and maintaining cool, dark conditions.  It is then available to be pumped automatically on-demand to the services required – including provision of fire-fighting reserves where needed.

Applied to a typical home, rainwater harvesting will provide the bulk of household non-potable water requirements (ie toilet-flushing, clothes washing and garden tap), thereby reducing mains water consumption by around 50 per cent. Used in public and commercial buildings that combine a large roof area with a high demand for non-potable water, even more significant savings are made – often leading to a capital cost payback period of as little as 3 years.  Enhanced Capital Allowance rules also provide a tax incentive for commercial applications.

Starting from the perspective of storm-water management, then the attenuation requirements will determine how much water needs to be retained on-site, and the rate at which it can be released into the site’s storm-drain or soak-away system. Given a regular high usage of the stored water for non-potable purposes, this can be taken into account when sizing the overall system, providing potential cost-savings.  Making subsequent use of the water for non-potable applications adds relatively small incremental capital cost, whilst contributing year-on-year savings on running costs.

Conversely, if the system is designed mainly from a rainwater harvesting perspective, then it will be designed to optimise the balance between the amount of water available for harvesting (itself a function of roof plan-area, local average rainfall, and mechanical/evaporation losses), the expected pattern of non-potable usage, and the desirability of regularly rotating the water in the storage tank.  Typically, this will not provide all the storm-water attenuation required on the site, but should make a useful “free” contribution to it.

Straightforward installation
The conceptual inclusion of a rainwater harvesting system in a design is very straightforward calling for no more than the underground works to bring down-pipe water to a single point for filtration and then entry into the storage tank.  Invert levels then also need to ensure that the storage tank can overflow into the broader storm-water management system during periods of prolonged heavy rainfall.

Arrangements also need to be made to top-up the storage tank during prolonged dry spells this, together with provision to services of non-potable water on-demand, being managed by a control panel making use of the system straightforward for the end-user, and indistinguishable in operation from using mains water for the same application.

On new buildings, using modern materials, this is extremely straightforward with the quality of the stored water being maintained by underground storage and efficient prior filtering.  High-quality, non-potable water results, that is then automatically fed on demand to services such as toilet-flushing, clothes washing machines and outside taps.

Independent monitoring by Severn-Trent Water and the Environment Agency on typical domestic installations showed that for the majority of the year rainfall keeps the storage tanks around half-full, with only occasional need to overflow into soakaways or use mains-water top-up.

It also showed that around half of all the water used by the householders was for non-potable applications.  In other words, the installation of a rainwater harvesting system reduced mains-water consumption by around 50 per cent.

Detailed system design is a matter for the system suppliers, the majority of whom, in the UK, are members of the UK Rainwater Harvesting Association (www.ukrha.org).  Although, as with all other building products, cost will certainly be a factor when choosing a supplier, by far the most important factors for a specifier to bear in mind are ease of installation, reliability in-service, and technical support.  Always bear in mind that the end-user will need their rainwater harvesting system to need no more maintenance than their other utilities, and to be just as reliable.

Increasing popularity
Even with extremely widespread use of rainwater harvesting systems they would have no noticeable adverse impact on the water levels available to the water supply companies. Therefore, it comes as no surprise that the UK market for systems has tripled in the last 2-years, with similar growth rate forecast for the current year.  This is a trend most likely to continue, given the ongoing Government review of national water management policy, and the support given for rainwater harvesting in the recent report of the House of Lords Science & Technology Committee.

The public sector, too, may well take the lead in helping to establish rainwater harvesting as a mainstream utility in the UK, given the suitability of buildings such as schools, hospitals, fire, police and ambulance stations, and military projects to exploit such systems.

Meanwhile, it is already clear that there is a re-dawning of the once widely practiced technique of harvesting rainwater in the UK, reflected in the 300 per cent increase in the UK market over the past two years. Continued market growth across the UK, particularly in the south of England, and consistent specification of rainwater harvesting systems in all new developments, will help to provide the medium-term solution to what otherwise will be a growing water-supply problem.

In summary then, rainwater harvesting provides designers and specifiers with a simple, reliable, easily-installed and cost-effective solution to their site water-related issues which needs to be at the front of their minds – just like any other utility – at the earliest possible design stage. Widespread adoption of rainwater harvesting will combine the twin virtues of substantially reducing demands on local water grids, without adversely affecting the water available to the utility companies for abstraction. It will also have the secondary benefit of saving all the energy currently wasted in bringing water up to drinking standard which is destined for toilet-flushing, garden irrigation and car/fleet washing.

Chris Williams is chairman of the UK Rainwater Harvesting Association, and managing director of Hydro International’s European operation.

Further Information ia available at www.ukrha.org