The national value case for saving water

This Issue This is a part of the Water use feature

By - , Build 105

In the last Build we reported on some of the findings from Beacon Pathway’s ‘national value case for sustainable housing innovations’. Here, we focus on water efficiency interventions in homes.

Last year, Beacon Pathway commissioned the National value case – a rigorous assessment of the value of six chosen interventions to improve the sustainability of homes (see Build 104 February/March 2008, pages 92–93). As the title suggests, the report aims to make the case (primarily to central government) for the national benefit of improving the sustainability of new and existing housing.

Each innovation was evaluated for four kinds of benefits: private economic benefits for households; environmental benefits (such as reduced pollution and CO2 emissions); social and other private benefits (including comfort and health); and national resource use efficiency. The case for intervention was labelled from ‘weak’ to ‘strong’.

The interventions were chosen on the basis of prior research undertaken by Beacon to determine realistic and affordable options that, in combination, would significantly improve the sustainability of a home.

Water and energy consumption linked

Water and energy efficiency are often considered independently of each other, yet both affect the environment, draw extensively on national resources and add to household running costs.

The collection, storage, transport, treatment, use and disposal of water have significant associated energy costs. Decisions to build a new water supply dam (as is currently proposed in Wellington), or to pipe water across the country to service urban areas like Auckland, have high capital costs and demand significant energy in their construction and operating processes. Such projects could be deferred, and ongoing costs reduced, by more efficient use of water.

Heating water consumes a great deal of energy in most households (around 30%). Measures to reduce water consumption (such as low flow showerheads) would mean less hot water was used, with a consequent reduction in both water and energy demand.

Benefits of improved water efficiency

There are strong arguments for improved water efficiency. Abstraction of water is costly. Using rainwater and greywater for non-drinking purposes, instead of potable water, would enable growth without putting pressure on existing supply systems.

If we used less water, we would also produce less wastewater – there would be a reduction in the financial and environmental costs of wastewater treatment and disposal. Given that councils spend almost a third of their operating budgets on managing potable water, stormwater and wastewater, there are also long-term benefits for ratepayers of greater water efficiency.

National value case assessments

The water-related interventions considered in the National value case were the use of low flow devices and appliances, and water metering and pricing (of potable water). The case for interventions to reduce the costs (financial and environmental) of heating water was discussed in our earlier Build article.

LOW FLOW DEVICES AND APPLIANCES

Three technical interventions were considered: low flow showerheads, dual flush toilets and water-efficient washing machines. When substituting for older, less water-efficient fittings and appliances, these three measures can collectively reduce water usage by about 25%. Although the capital cost of introducing these changes is minimal, the benefits are significant. It is hard to calculate a direct cost saving for most households as most do not directly pay for water by volume (although it is a substantial proportion of council rates bills), but the national cost savings are clearly significant. There is also an energy saving for households as a result of reduced demand for heated water.

The case for intervention was found to be ‘medium–strong’. Only the lack of social benefits prevents a ‘strong’ rating.

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METERING AND VOLUMETRIC PRICING

The case for extending water metering to the remaining 65% of the mains-supplied population is also calculated as ‘medium–strong’, but for different reasons. Here, the greatest value is in the national resource efficiency savings, rather than in direct benefits to householders.

The main reason to introduce water metering is to give clear price signals to consumers, providing them with an incentive to reduce wastage. Currently, the cost of water is ‘hidden’ by being charged through property rates. There is no incentive for individual households to cut usage because rates charges are calculated against the use of ratepayers as a whole. Introducing water charges would provide householders with the information needed to make choices regarding water consumption, with consequent financial savings for greater efficiency.

Private economic benefit will depend on the extent householders’ bills for water are offset by lower property rates. Research in New Zealand and overseas indicates that the introduction of water metering has a significant impact on water use, with up to 30% savings. If this figure were extended to the nation as a whole, the savings would be significant.

Saving millions of litres possible

The report concludes that the introduction of these measures, from a national resource use efficiency perspective, is ‘virtually costless’. And yet they would significantly reduce national water consumption, with low flow devices and appliances alone resulting in a 96 million m3 saving in water use each year (and an associated reduction in energy consumption).

There is clearly a compelling case for government intervention in the form of incentives for householders and more stringent compliance requirements for new-build and renovation projects.

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For more

You can download the ‘National value case for sustainable housing innovations’ from www.beaconpathway.co.nz.

Download the PDF

Articles are correct at the time of publication but may have since become outdated.

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