Water usage in the Auckland region should be reduced by 15 per cent by 2025, a draft plan has recommended.
The reduction on the present water demand of 330 litres a day per person should be achieved despite population growth.
The report says a further 10 per cent
saving could be achieved by treating and recycling water that had been used and substituting drinking water use with other sources, such as stormwater collected in rain tanks, grey water, bore water for industrial and external use and /or treated wastewater.
The plan for managing drinking water, wastewater and stormwater services in the 90 years ahead, when Auckland could have 3.5 million people, is being placed before councils and public for comment.
Watercare, the region's bulk water and wastewater service provider, is leading work on a draft plan which could involve spending of $20 billion to $40 billion over the period.
Presenting the final draft to the Auckland Regional Council yesterday, Watercare chief engineer Jim Hodges said encouraging more efficient use of drinking water might delay or defer the need for some major works in the next 20 years and have less effect on water bills.
Use of treated wastewater as a direct substitute for A grade drinking water was technically feasible but direct use of it for drinking was not part of the current plan.
Pumping more water from the Waikato River would be $200 million cheaper than developing a source in the hills and rivers north of Auckland. However, there were worries about the energy costs in pumping and relying too much on the southern source, in case of a volcanic eruption.
Mr Hodges said the transfer and treatment of wastewater must be boosted to meet environmental standards and to reduce the number of raw sewage overflows. But expanding the Mangere plant, on the Manukau, offered the greatest opportunity to reduce sewage overflows in dry and wet weather.
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