Householders in the South-East saved more than 9,500 million litres of water last month.
The Environment Agency has said that all water firms saw a reduction in use because of the drought.
Hosepipe bans are in force across Sussex. The county's main water provider, Southern Water, has permission to impose stricter restrictions under a drought order if needed.
Each day in June, people in the South-East used 300 million litres a day fewer than usual.
Howard Davidson, the Environment Agency's southern region director, said: "It's really encouraging to see that demand for water is down.
"June was a hot and dry month and we would normally have expected to see water use soar.
"It seems that people are being restrained in their use of water and this all helps reduce the amount we need to take out of the environment and ensure that there is enough for later in the year.
"We've still got most of the summer to go and it looks as though it's going to be a hot one.
"We all need to save water wherever we can and there is always more that we can do.
"Although reservoirs in the region are looking healthy at the moment, they don't paint an accurate picture of our water resources situation.
"Seventy per cent of our water comes from under the ground.
"What we can't see from the surface is that many of these supplies are very low."
Barrie Clarke from Water UK, which represents water companies, said: "We've been working hard to keep customers up to date on the drought so it's really good that people are using less water.
"There aren't any magic solutions to a drought this serious.
"We all have a part to play in making our scarce water go further at home and at work."
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