The pledge was expected to be made in the Thames Gateway delivery plan, due to be launched after Planning went to press.
Environment Agency head of sustainable development Julie Foley said this would be the first time that such a commitment has been made at a development level.
Its report shows that it is possible to build 165,500 homes with no overall growth in water demand solely by using conservation methods, despite the gateway being severely water-stressed.
The findings, published at the Thames Gateway Forum, urge greater water efficiency in new schemes and retrofits to existing buildings.
Foley, who led the study, told Planning: "The focus is very much on demand management and water efficiency rather than new reservoirs."
Planners should consider requiring homes to meet levels 3 to 4 of the code for sustainable homes in water- stressed areas, she added.
Measures such as com- pulsory metering and low-flush toilets are also more cost-effective than tackling leakages, according to the report. The £275-£765 estimate per new home is less than one per cent of the overall cost for the developer. The agency hopes that the work will also inform the development of eco-towns.
The report is available at PlanningResource.co.uk/doc.