The rainwater harvesting market in Germany is 300 times that of the UK, contends Lutz Johnen, a founding member of the UK Rainwater Harvesting Association. This alternative water supply plays an important strategic role in the overall German approach to water management.
Lutz Johnen
Three unusually dry winters, followed by a long hot summer, have served to remind everyone of the fragility of UK water supplies, particularly in the south of England where the water available per capita is less than can be found in many Mediterranean and Middle East countries. The inevitable outcome has been the selective but widespread imposition of hosepipe bans allied to a positive blitz of media coverage. This media attention is usually aimed critically at the perceived excessive profits of the utility companies concerned, and their inability to meet water leakage targets.
Why then are similar pressures not being felt in countries such as Germany, where the constraints on water supplies are much greater than in the UK? The answer, very simply, lies in Britain’s best-kept secret, rainwater harvesting, long since discovered in Germany to be at least part of the answer to that country’s water supply problems.
Although scarcely mentioned throughout the current water-shortages debate, the harvesting of rainwater, for subsequent household and commercial use, was once widespread throughout the UK. The practice, however, all but ceased with the introduction of clean, inexpensive tap water supplied via the mains.
Modern rainwater harvesting is no different in principle to the systems still installed on many 19th-century houses throughout the UK. Rain falling on the roof is channelled to a storage tank from where it can be pumped for non-potable use (typically toilet-flushing, clothes-washing and outside taps) as and when required. Modern technology simply introduces easy-to-install storage tanks, high quality filters to ensure water-quality and automatic controls/pumping, to ensure that from the user’s perspective the water supplied is no different than using mains-water.
The water available through rainwater harvesting, almost exactly matches household requirements for non-potable water; a typical 4-bed house, for example, has the potential to supply around 60,000 liters per year in even the driest parts of the UK – broadly matching the non-potable demand. This in turn displaces the mains water that would otherwise be used, in the process making commensurate savings on metered water costs and saving the energy that would otherwise be wasted bringing water destined for toilet flushing up to drinking-water standard. So it is good for global warming too!
The same principles and techniques applied to public/commercial buildings that combine large roof areas with a high-demand for nonpotable water can produce even more spectacular savings, compared to domestic dwellings. The storage tanks for such applications can also support the overall stormwater management of developments by attenuating heavy rainfalls, thus helping to reduce downstream flood risks.
