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Half of all water use is accounted for by buildings.

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The imperative to consume less fossil fuel, and the related problem of global warming, have biased sustainable design in favour of preserving energy. Other resources, particularly water, have been overlooked. Yet water is arguably more important than energy, especially for biodiversity, food production and public health. And, like energy, water supplies are finite, promising long-term stress as demand increases.

Some in the eu predict that Europe will run out of water by 2015. uk water use is currently increasing by 2 per cent per year, and the National Rivers Authority thinks demand in this country will exceed supply by 2021. The eu is anxious to put in place a water framework directive which would provide the power to create a pipeline for transferring water from the wet north to the drought-ridden south of Europe.

What has this to do with architects? Because buildings are the main means by which water is consumed within the uk - 50 per cent of all water use is building-related (the figure mirrors closely that of energy) - the stress on supplies can be reduced by designers taking measures to conserve water just as they already do for energy.

Global supplies

The problem of water stress lies in matching demand and supply. As global warming bites, rain falls in different places and at different rates. Recent forest fires in Indonesia, Mexico and Brazil are partly the result of geographically displaced rainfall. In areas of southern France it has not rained for nearly two years, yet Scotland's rainfall is rising.

Addressing global warming through design also helps address global rainfall. But in the short term problems remain for many industrialised countries. Increasingly, borehole extraction is used to top up reservoir supplies, but this 'fossil' water is itself a limited resource. In Europe, deep groundwater is the main source of supply for many arid regions. As more is used for agriculture and in tourist developments, groundwater levels fall, putting forests, marshes and heathlands under stress. The greatest threat to biodiversity comes not from development per se, but from resulting changes in the water regime. And biodiversity, locally and globally, is one of the best indicators of the sustainability of development.

Action for buildings

In the uk, water shortage is not primarily a problem of changing rainfall patterns but of the changing way we live. Homes use more water than ever before to serve our appetite for health, cleanliness and gardening. Our domestic white goods consume a great deal of water. We have smaller households in more homes. In fact, so much water is used in modern homes that for some energy-efficient dwellings the annual water bills exceed those for gas or electricity.

Although 50 per cent of water is used in buildings, little is for drinking and cooking. Domestic water consumption is divided between:

drinking and cooking (6 per cent)

flushing wcs (20 per cent)

baths and showers (12 per cent)

laundry (5 per cent)

dishwashing (3 per cent)

gardening (2 per cent)

others (2 per cent).

Architects can have an impact by addressing the growing demands for water. The principles which apply to water conservation are much the same as for energy conservation - reduce demand, recycle, and exploit renewable supplies. Demand can be reduced by specifying low water-using appliances, exploiting new technologies such as vacuum wcs and taking simple measures to reduce waste (such as using self-closing taps).

As with many environmental benefits, the extra costs do not always justify investment by the usual standards of rate-of-return. With water in the uk still relatively cheap, the additional costs of low-flush wcs or recycled greywater systems are a serious deterrent.

Greywater systems are the answer, in theory, since it makes little sense to use drinking-quality water to flush wcs or wash clothes. However, for a system to make economic sense it would have to be shared between at least 15 dwellings. So it is projects like the Millennium Village at Greenwich (1400 homes) or Ecolonia in Holland (300 homes) which are the test beds for the new water technology. Greywater recycling requires high levels of maintenance to prevent the adverse microbiological reaction which can pose health threats or damage drainage systems. With greywater systems costing at least £1200 per house, the benefits for new-build are not yet proven, and for existing buildings their retrofit costs are prohibitive.

However, two changes are on the horizon. Water is due to increase in price above the level of inflation over the next few years (to pay for infrastructure improvements and to meet rising eu standards on water quality). And as water technology improves, the cost of environmentally friendly systems falls. So within the life of a building (or at least the life of a bathroom), it makes sense to specify some green water products, from spray taps to sensors in urinals.

The increase in domestic water metering has focused attention on water consumption. Simple measures available on the market at no great additional cost can save a typical household 30 per cent of their water bill, although improvements above this level become less cost-effective. A totally water self-sufficient house could cost £3-5000 above the norm and, with maintenance costs, the additional investment might not be retrieved within the life of the building.

Great savings can also be made in water consumption in the commercial sector. Improvement in wc design (such as variable flush), valve cistern filling (as against siphonic systems), urinals which employ chemicals rather than traditional water flush, infra-red person sensors at handbasins, etc, are all viable outside the domestic field.

In the commercial, educational and hotel sectors there are measurable benefits (environmental and financial) in taking water seriously. bsria and bre are currently working on guidance to designers. The Environment Agency (the main government body responsible for water) is soon to publish a study on water conservation which will have implications for architects.

Designers need to face up to the challenge of water just as they must for energy. As the rspb recently warned, we may lose our best wetlands if ground water levels continue to fall, leading to significant loss of biodiversity in the uk. With buildings using half of all water, architects have a role to play in saving the bittern.

Brian Edwards is professor of architecture at Huddersfield University and a member of the riba Energy and Environment Group. Thanks to Richard Nicholls at the University of Huddersfield for help with this article

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