Water
Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.
Minimising Water Use
Careful design and specification can reduce the amount of water used in a home and save energy costs without inconveniencing the people who live there.
Low pressure / high pressure
One of the first influences on water usage is whether a low pressure, unequal pressure, or high pressure household water system is chosen. For example with a low-pressure hot water system a warm shower flow averages seven litres per minute while a mains pressure shower averages 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.
Too high a pressure 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.
Too low a pressure can mean:
- lower water usage
- poor flow at shower heads
- it takes a long time to fill baths and tubs.
Hot water system design
You can design and build a system which requires less water to be run off before the hot water arrives, by:
- locating the hot water storage tank close to kitchen and bathrooms
- installing more than one hot water storage tank or water heater where points of use are far apart
- insulating the pipes to reduce heating costs (but this has less impact than reducing pipe lengths).
- Avoiding waste through long hot water pipe runs
A lot of water can be wasted while occupants run a tap waiting for hot water to come through. Shorter pipe runs save both water and energy.
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 six-litre/three-litre dual-flush cistern (usually a new pan is needed). For existing toilets, where fitting a new pan is impractical there are many options available to consumers to reduce water usage.
In all cases sufficient flushing water volume must be maintained to ensure the pan is cleared with a single flush.
Reducing water flow
Water usage can be reduced by specifying/installing:
- low-flow shower heads which use nine 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 fitting.
- 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 larger volume of water is required.
Specifying efficient appliances
Water use can be reduced by:
- not specifying/installing waste disposal units – the owner can compost all organic kitchen waste
- recommending water-efficient appliances.
For general advice on choosing appliances, see appliances. You can compare water efficiency ratings for appliances at www.waterrating.gov.au and www.wsaa.asn.au. Though these are Australian websites, many of the appliances they refer to are commonly available in New Zealand.
Landscaping
It is estimated that between 10 and 30 percent of household water use takes place in the garden. Architects, designers and landscape architects can reduce the demand for irrigation by encouraging a style of garden which doesn’t require extensive irrigation.
What householders can do
For more info on what consumers can do, refer them to www.smarterhomes.org.nz/water.