Water is an increasingly scarce and precious resource. Rising demand, water pollution and climate change are a huge threat to fresh water supplies. The construction industry has acknowledged the urgent need to conserve and manage water and has taken measures to implement sustainable water design throughout the build process.
Water conservation in buildings is achieved partly through effective plumbing design. A gravity hot-water system delivering low pressure water uses less water than a mains pressure hot-water system. Installing point of use water heaters ensures that cold water is not wasted while waiting for hot water to come through the taps. Well-lagged and properly positioned pipes will also help keep water hot. Along with plumbing design, water conservation is achieved through the specification and installation of water-efficient appliances and fittings.
Conventional flush toilets are responsible for up to 40% of domestic water use. Putting a displacement device in the cistern will save some of this water, but a more efficient solution is to fit a low-flush toilet, that uses less than 4 litres of water per flush, cutting use in half. There are many different models including: dual flush toilets, with a lower flush option for fluids and a standard flush level for solids; gravity toilets, that depend on gravity alone; and pressure assisted toilets that combine gravity with compressed air. Dry composting toilets are the most water-efficient toilets on the market, using no water at all.
Taps and Fittings
Washbasins and sinks are responsible for around 8% of domestic water use. Conventional twist taps use around 4 litres per hand wash; water efficient fixtures can reduce this to 2 litres or less. There are a number of fixtures available for washbasins, sinks and bathtubs: including push taps and sensor taps (self-closing so taps aren’t left running), spray taps (reduce flow volume), and other flow regulators and restrictors (restrict flow, regulate pressure and reduce the force needed to turn the flow off).
Showers account for around 20% of domestic water use. Showers are generally considered to be more water-efficient than baths, with the exception of modern power showers. Regular showerheads use around 20 litres per minute, and replacing this with a low-flow showerhead will reduce this to less than 10 litres per minute, by creating finer drops or using pressure powered aeration.
Installing a high efficiency dishwasher saves water and energy. Water efficient dishwashers use around 16 litres of water per load compared to 40 litres for hand washing dishes.
These account for about 14% of domestic water use, High efficiency models use less than 50 litres per load, older models use over 100 litres. A full load is always more water efficient than a half-load. In the UK all new washing machines and dishwashers are graded with an energy label (A uses the most energy and water, and G the least).
Rainwater Harvesting Systems
Water can be collected from roofs and recycled for many purposes including flushing toilets, filling washing machines and watering gardens. There are a wide range of rainwater harvesting systems available, most of which collect water from the roof via a drainpipe, filter out leaves and other debris, and store water in a tank. Using a simple rainwater butt can save significant amounts of water for watering the garden. More advanced models can be used in conjunction with existing mains systems, and many will pay back their costs in as little as two years.
Waste Water Recycling
There are two kinds of waste water in domestic buildings: greywater and blackwater. Blackwater comes from toilets, and contains harmful pathogens. It must be properly treated before being discharged into the environment. Both blackwater and greywater can be effectively recycled on-site using constructed wetlands or reed bed systems.
Greywater comes from baths, sinks and showers and can be recycled and reused for watering the garden or flushing toilets. Reusing greywater for flushing toilets can save up to 50% of domestic water use, but requires some form of treatment such as filtering and disinfectant to remove bacteria and other biological material. If used directly for watering the garden, greywater can be left untreated, but only biodegradable, non-toxic household cleaning and toiletry products should be used in the water system. Other fats and additives might need to be treated for garden use, and the soil should be tested regularly for nutrient and chemical composition. Greywater systems range from advanced commercial designs to DIY self-built models.
Strategy for a Sustainable Future
The sustainable building movement is working to reduce, reuse and recycle domestic water use, bringing huge savings in energy and water, and reducing the environmental impact of both water disposal and the need to pump water over long distances. This has a positive impact on carbon emissions helping to combat climate change, and mitigates the threat of impending water shortages. Sustainable water design is an essential strategy for safeguarding our future.