Thames Water has thanked its customers after demand in June dropped by 176 million litres a day.
Thames Water is London's largest water supplier
It is the equivalent of London's six million customers, under a hosepipe ban since April, saving enough water to fill the Royal Albert Hall.
Earlier this month the firm was told by regulator Ofwat to invest an extra £150m to replace ageing pipes.
It was expected to cut the daily leakage to 860 million litres but only managed to reduce it to 894 million.
The firm has missed targets three years in a row, and has been criticised as water supplies fell and profits rose.
THAMES WATER LEAKAGE
In millions of litres per day:
Thames Water said the month of June recorded only a quarter of the usual rainfall.
On average, London's water demand is lower by 5.3% since the hosepipe ban came into effect on 3 April, with 118 million litres saved every single day.
Thames Water's Duncan McCombie said: "We want to say a big thank-you to all our customers who have been saving water during the drought, but with July temperatures soaring we do very much need them to keep up the good work.
"We know June's fall in demand can't simply be due to the hosepipe and sprinkler restrictions, because only four out of every 10 of our customers own a hosepipe.
"It just goes to show that if everyone makes small changes to their daily routines, such as only switching the washing machine or dishwasher on when they are full, it can help make a big difference."