Water water everywhere (except where it's needed)

The south-east of England is in the grip of a serious drought with rainfall since November 2004 well below average, and some places at their lowest levels for 85 years. For London, 2005 was the third driest year on record. Groundwater levels are the lowest since records began and some reservoirs in Kent and Sussex are at 35% of capacity, and the prospects remain unpromising for the rest of spring and summer to make up this shortfall. Hence the Environment Agency has called on the water companies to introduce drought plans, including restrictions on non-essential uses, such as watering of gardens and window cleaning.

There are parts of Britain that do get plenty of rainfall - Scotland, for example, received a total of 1686 mm in 2004. On the other hand, the Anglia and Thames regions both only had around 700 mm - less than Istanbul, Rome or Dallas.

Assessing the water supply

One problem is that what comes down doesn’t necessarily end up in our pipes. Only 5% of precipitation becomes available for water supply. This low capture rate can be explained by the intensity of rainfall, the efficiency of capture, characteristics of drainage routes and geology, and the number of reservoirs and boreholes. Yet more may be lost through evaporation, or may soak into the ground or run off into rivers and the sea.

Where is it all going?

Likewise, much of what is available for water supply won’t find its way into our taps and cisterns. In European cities, between 30 and 80% of the supply is lost through leakage. In London in 2002, some 865,000 m3 of water were lost per day - the equivalent of 300 Olympic-size swimming pools and representing a quarter of all leakage in England and Wales. Thames Water is spending some £3.5bn on water infrastructure repair and replacement - a major undertaking bearing in mind that 50% of the pipework was installed more than 100 years ago, while a third is 150 years or older. The task is made more difficult by the sheer complexity of infrastructure underground, and the lack of detailed information on what is buried under our roads and pavements.

In London in 2002, some 865,000 m3 of water were lost per day – the equivalent of 300 Olympic-size swimming pools

 

It could be argued that if water companies were more efficient at capturing rainwater and, once captured, didn’t allow most of it to leak away, there would be no need for the consumer to worry about how much water they use. However, in the real world there is increasing focus on demand management, with the onus on the incorporation of water-saving devices to reduce consumption.

The main sectors that use water are agricultural, industrial, commercial and residential. Most agricultural and major industrial users require non-potable water and abstract this from rivers and boreholes. Use of water for domestic purposes - hot and cold water services - represents some 64% of overall demand. Most non-residential users have metered supplies, although 80% of householders in the UK do not have water meters. This compares with only 10% in other European countries. There is clear evidence from trials E E commissioned by the Environment Agency that metering reduces demand - typically by 10-20%. Resistance to making metering a statutory requirement remains, however, although most new dwellings and commercial/industrial buildings are fitted with water meters.

BRE determined that for dwellings the average water consumption per person in the UK in 2000 was approximately 160 litres/day, the equivalent to around 59 m3/bedspace per year. Despite improvements in water efficiency, this is some 50% more than in 1975. This is likely to be due primarily to the greater and more frequent use of power showers and the greater propensity of dishwashers.

Unlike energy demand - limited by Part L of the Building Regulations - no statutory limits on water consumption exist. Buildings assessed under BREEAM (Building Research Establishment Environmental Assessment Method) and EcoHomes - the version for dwellings - are assessed for predicted water consumption. However, the benchmarks are not mandatory and trade-offs are allowed with other credits, which means that a building with no water-saving measures at all can still perform well under the assessment protocol.

Solutions do exist

Water shortages are not going to go away and climate change is likely to make the problem steadily worse

 

On the other hand, the draft Code for Sustainable Homes incorporates a maximum standard of 125 litres/day per person, which equates to 46 m3/bedspace/year - equivalent to one credit out of a possible five under the 2005 version of EcoHomes. This will soon become mandatory for all social housing requiring Housing Corporation funding, all English Partnerships developments - such as the London Wide Initiative - and all ODPM housing growth programme funded developments.

The measures required to achieve this are relatively simple and cost effective (see Six points you should consider when designing water systems, left). In fact, if the developer or householder can be persuaded not to install power showers, then a cost saving is possible. It is often presumed that WCs place the greatest demand on the water supply to a dwelling - typical use per bedspace is around 39 litres/day for a 6 litre cistern. However, a power shower can consume more than 15 litres/minute with typical use around 80 litres/bedspace/day. Aerated shower heads on the other hand might typically use around 26 litres/bedspace/day (68% lower than a typical power shower).

Other water-saving appliances include:

• 6/4 litre dual flush WC cisterns - 30% lower water consumption than 6 litre cistern
• A+ rated washing machine - 33% lower than typical
• A+ rated dishwasher - 50% lower than typical
• Spray taps for hand washing - 50% lower than standard pillar taps

Waste water recycling and rainwater harvesting can also potentially save significant volumes of water. For a single house the simplest and cheapest way of harvesting rainwater is by connecting downpipes to a butt, the contents of which can be used for irrigation. For larger buildings roof run-off can be piped to a below-grade tank and the water filtered, treated and supplied to urinal and WC cisterns as well as used for irrigation. Grey water recycling on the other hand re-uses waste from wash basins, showers, baths and white goods, again usually for toilet flushing, although more sophisticated water treatment is required because of the risk of microbial growth in the waste water. These latter systems are available for individual houses, but maintaining water quality is an issue.

Water shortages are not going to go away and climate change is likely to make the problem steadily worse. A major programme of leakage repair and replacement of Victorian infrastructure is under way but it is also essential that developers and consumers take responsibility for demand management. Hopefully, the government will introduce legislation both to make metering mandatory and to set consumption limits on the same lines as Part L of the Building Regulations.