Sustainable water use and drainage

Advice when planning to carry out construction work to effectively reduce water usage in buildings.

Households are the biggest users of water - 55% of all water used in the UK. We use an average of 150 litres of water per person per day, of which 35% is flushed down the toilet (OFWAT & Environment Agency).

Also, the large number of new houses which are planned to be built over the next few years will increase the competition for available water between the environment and people, especially in the South East of England which has been designated an area of ‘high water stress’.

The effects of excessive water use on the environment are considerable. This includes over-extraction from rivers and boreholes and overburdening of existing sewage systems.

This leads to increased overflows, an increase in the amount of energy needed to treat water and a general deterioration in water quality. It is therefore clear that a more prudent use of our limited water supply is essential in order to reduce the impact on our natural ecosystems.

There are many effective ways to reduce our demand on mains water, solutions include:

  • Reducing water usage;
  • Using alternative sources of water such as rainwater;
  • Recycling grey water (waste water from baths, shower and wash basins);
  • Recycling black water or sewage, although this is not possible in all locations.

Many of the above solutions will also have an impact on our overburdened sewage systems by reducing the volume of water discharged into the sewage system.

Additionally, on-site treatment systems (where appropriate) will also help to reduce the burden.

Reducing water usage

As the toilet is the largest contributor to water use in the home it seems a good place to start reducing water. There are a number of ways which this can be done.

Low flush or duel flush toilets which use 3-4 litre flush compared with the old style cisterns (pre 1993) which can use up to 9 litres per flush. If you have an old cistern and do not wish to replace it you can simply fit a water saving device. These can save 1 to 3 litres per flush.

When installing or replacing showers and taps look for models with water saving features such as aerating heads. These can save up to 80% of the water used in ‘ordinary’ taps. Having a quick shower uses a third of the water that a bath does but, don’t be fooled, power showers can use more water than a bath in less than 5 minutes.

New washing machines are much more water efficient and use about half the water of older models, similarly dishwashers are now becoming much more water efficient. Be sure to check the EU labels when purchasing new white goods for your home.

Rainwater harvesting

One way to decrease water demand in your property is to use a rainwater harvesting system to provide water for domestic uses that do not require water treated to drinking quality.

A rainwater harvesting system can reduce mains water use by 33% when using rainwater to flush toilets and can be installed into new and existing buildings. Rainwater harvesting also aids sustainable drainage as it reduces storm water discharge rates.

The simplest method to harvest rainwater is to install a water butt and connect it to a downpipe from the roof via a diverter – water collected is suitable for garden use and can save a large amount of money if you have a metered supply.

Another method is more complex and called a rainwater system. Water is collected in an underground tank and then filtered in various ways and pumped back to the house to be used for appliances or to go into the loft header tank.

However, in order to render rainwater suitable for drinking it must be passed through a UV sterilisation unit.

Greywater recycling

Greywater is water which is produced from baths showers and washbasins (not toilets). It can be collected in a household reuse system and treated to a standard suitable for WC flushing.

Greywater recycling could give the potential for savings of up to a third of the daily household demand. Untreated greywater can also be used for watering the garden if used immediately after it is produced.

Blackwater recycling

Where the building is in an urban environment, treating sewage (referred to as black water or foul water) on-site may not be a possibility. In more rural environments systems such as septic tanks, cesspools and reed beds can be considered. These systems use reeds to naturally filter out pathogens and the discharge is safe to distribute over the land.

Permeable paving

Permeable paving allows rainwater to percolate through the paving and into the ground before it runs off.

All permeable paving systems consist of a durable, load bearing, pervious surface overlying a crushed stone base that stores rainwater before it infiltrates into the underlying soil. The marked benefit of permeable paving is that it can markedly reduce flooding.


Any alterations or new build are likely to need a Building Regulation application and may need Planning Permission. The Building Regulations which specifically relate to water and drainage are Part G: Sanitation, hot water safety and water efficiency, and Part H: Drainage and waste disposal.