Water
Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.
Minimising water use
As the population increases, demand on the water supply also increases. Reducing the amount of water that we consume will help control the demand on our water supplies.
As well as ensuring the building owner is aware of the impact their behaviour, water use can be minimised by:
- controlling water pressure
- designing an efficient hot water system
- controlling water for toilet flushing
- reducing water flow from outlets
- specifying efficient appliances
- careful considerations when landscaping.
Controlling water pressure
You can significantly reduce water usage depending on whether a low pressure, unequal pressure or high pressure household water system is selected. For example, a low pressure hot water system shower flow will average 7 litres per minute, while a mains pressure shower will average 12.5 litres per minute.
Water pressure in local authority pipes varies, but the pressure in a household system must be controlled. Getting the pressure right will ensure convenience and comfort without waste.
A pressure that is too high can result in:
- higher water usage
- high wear and tear on valves.
A pressure limiting valve installed on the main supply line can be specified to moderate high pressure.
A pressure that is too low can mean:
- lower water usage
- poor flow at shower heads
- baths and tubs taking a long time to fill.
Designing an efficient hot water system
You can design an efficient water heating system that will reduce household water usage by including features such as minimising hot water pipe runs and specifying low-flow devices.
Design a system that requires less water to be run off before the hot water arrives at the fitting by:
- locating the hot water storage tank close to kitchen and bathrooms
- installing a continuous-flow hot water system, particularly for remote outlets, so that hot water does not need to be stored
- insulating the pipes to reduce heating costs (but this has less impact than reducing pipe lengths).
- Avoiding waste through long hot water pipe runs
If a kitchen is remote from the hot water storage system, install a secondary continuous-flow system to reduce water wastage.
Controlling water for toilet flushing
In an average home, up to 30% of water use is for toilet flushing. This can be reduced by:
- ensuring a dual flush cistern is specified
- installing a water-efficient toilet pan
- using collected rainwater for flushing
- using treated greywater for flushing
- installing waterless composting toilets where no mains sewer connection is available
- Modern cassette flushing units are adjustable for both half and full flush options.
Many older cisterns use far more water than necessary – typically 12 litres is used. To reduce the amount of water the cistern releases, specify/install a modern 6-litre/3-litre dual-flush cistern. (A new pan may need to be installed where a dual flush cannot be fitted to the existing WC pan.)
For existing toilets where fitting a new pan/cistern is impractical, options you can use to reduce water usage include:
- placing an object such as a brick, or plastic milk bottle filled with water that has the top firmly screwed on into the cistern to reduce the amount of water required to fill an older cistern.
- adjusting the float ball by bending it down slightly to reduce the volume of water in the cistern – ensure that sufficient flow and volume is maintained for an adequate flush
- ensuring that the cistern supply shuts off fully when not in use.
In all cases, sufficient flow and volume must be maintained so the pan is cleared with a single flush.
Reducing water flow from outlets
Water usage can be reduced by specifying/installing:
- low-flow shower heads that use 9 litres of water or less per minute and still deliver a comfortable shower
- aerators on taps used for hand washing – aerators are not suitable for taps on fixtures such as baths where water is being used to fill the fixture.
- Reduced water flow by specifying an aerator
An aerator on a tap used for handwashing will reduce the flow while still providing plenty of water. Aerators should not be specified for taps on fixtures such as baths where a large volume of water is required.
Specifying efficient appliances
Reduce water use by recommending water-efficient appliances.
Do not specify or install waste disposal units. Instead, where possible, compost all organic kitchen waste.
An Australian water efficiency labelling and standards (WELS) scheme that tests and labels appliances is available at www.waterrating.gov.au. It allows a comparison of water efficiency ratings of appliances to be made by providing:
- total water consumption given in litres and as a star rating
- a star rating for efficiency – the more stars, the greater the efficiency. (The rating label will also give annual energy consumption for a given operating cycle.)
New Zealand water efficiency labelling regulations came into effect in July 2009, and all new products are required to be tested and labelled by 1 July 2010. The scheme is similar to the Australian scheme.
More information can currently be found at www.mfe.govt.nz/issues/water/wels-scheme.html.