A scorching Bank Holiday heatwave led to more than one billion litres of extra water demand across the region.
Thames Water recorded more than one billion litres used across London and the South East over the long weekend, with temperatures reaching a peak of 35.1°C at Kew Gardens.
In some areas, water usage in homes with gardens increased by as much as 50 per cent, driven by outdoor activities like filling paddling pools, watering plants and using hoses.
The sharpest rise came on Monday, when demand reached 2,140 million litres in London alone - 252 million more than usual.
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Thames Valley and the Home Counties also saw significant increases, hitting over 740 million litres per day, 135 million above normal levels.
A Thames Water spokesman said: "We are investing in the biggest upgrade to our network in 150 years, replacing and strengthening pipes and infrastructure to reduce leaks and improve resilience.
"At the same time, our teams are working around the clock to keep supplies flowing today, fixing hundreds of leaks every week, monitoring the network 24/7 and moving water to where it is needed most."
The company has urged residents to take simple steps to reduce water use during future hot spells, especially outdoors and during peak times.
Thames Water recommends swapping hoses and sprinklers for watering cans, avoiding daytime watering, reusing leftover water from sinks, and using buckets instead of hoses for washing cars.
Letting lawns go golden during dry periods is also suggested as a water-saving measure.
