The plant would be used mainly during droughts
London's mayor has withdrawn a legal challenge to a desalination plant in a deal with Thames Water that aims to keep traffic moving in the city.
The planned £200m facility in Beckton, north-east London, will make supplies from the Thames estuary drinkable.
Previous mayor Ken Livingstone launched the challenge against the plant on environmental grounds despite the government giving it the go-ahead.
Mayor Boris Johnson said the deal would cut the impact of roadworks on traffic.
He said "wide-ranging measures" would include setting up pilot projects across the capital to look at different ways of working in the city's streets.
Mr Johnson said the company had also agreed to new environmental measures.
These include helping to capture and reuse the waste energy generated by the proposed Barking Power Station to help provide heating and hot water for up to 90,000 homes and save up to 90,000 tonnes of CO2 a year.
Mr Johnson said: "Roads must not be cordoned off when no-one is working there, so Londoners will welcome Thames Water's commitment to help get cars moving again.
"This will help to reduce congestion and drivers' frustrations throughout London."
Mr Livingstone had overturned Newham Council's decision to grant permission for the plant saying it would increase carbon emissions and that Thames Water should concentrate on fixing leaks.
An inquiry was held last year into the scheme and the government then gave it the go-ahead but Mr Livingstone said he was still pursuing a legal challenge.
Darren Johnson, Green Party member on the London Assembly, said: "Building the desalination plant is the kind of short cut which we have come to expect from Thames Water.
"Instead of spending money on this energy-wasting, short-term solution, they should be investing in fixing pipes and stopping leaks."
Thames Water said the plant could supply 140 million litres of water a day, enough to supply 400,000 homes in north-east London.