Water companies are warning Sussex faces even tougher supply-saving restrictions because the heatwave is making drought conditions worse.

Hosepipe bans and other drastic measures are increasingly likely across the county because people are rapidly sapping up the remains of a dwindling water supply to cool down in the sizzling summer sun.

Water companies said they were disappointed people were not heeding the advice and helping to conserve limited supplies. Others urged the county to adopt a "Dunkirk spirit" and pull together to avoid the crisis of a summer drought.

The sweltering conditions at the weekend put a major strain on resources and water firms say if this carries on, they would have no choice but to ban hosepipes and sprinklers throughout the county.

Weathermen are predicting the heatwave is going to last.

Water companies say they could even have to resort to cutting water pressure and switching off supplies to homes on a rotation basis.

Millions of extra litres of water were used at the weekend by householders desperate to rehydrate and feed their sweltering gardens.

Demand shot up by up to 20 per cent, even in places where customers have been warned to use less water.

Southern Water, which imposed a hosepipe ban in its northern area on June 9, said it was disappointed customers had not listened to warnings, especially following the second driest winter in 100 years.

Temperatures on Sunday reached 28C (82F), the hottest so far this year.

Householders in the Southern Water region, which covers most of Sussex, responded by using 699 million litres of water that day, 89 million more than they were using per day in the middle of last week.

In the South-East Water region of East and Mid Sussex and parts of west Kent, customers used 213 million litres compared to the usual 190 million.

Penny Hodge, for Southern Water, said: "Last weekend we saw the biggest increase in demand so far this year. We are disappointed it rose that high.

"Our advice is there are other ways where you can still have a thriving garden without using lots of water on it."

She said the hosepipe ban appeared to have made little difference to the amount of water people were using in north Sussex, where reserves are lowest.

"If we continue to see such a high demand, we may have to use increased restrictions."

Southern Water has not taken enforcement action before because people have obeyed bans but it says it will have no other option if people continue to disobey restrictions.

Jane Gould, spokeswoman for South East Water, said: "Levels in Ardingly and Arlington reservoirs are at about the 90 per cent mark. Flows in rivers are starting to drop.

"It is something we are having to monitor on a day-by-day basis."

Keith Taylor, leader of the Greens on Brighton and Hove City Council, said: "It is beholden to everybody to use resources sensibly.

"I have always obeyed bans. It is the old Dunkirk spirit. Maybe there is a new 'I'm all right, Jack' spirit."

An Environment Agency spokeswoman said: "The Department of Health recommends during a heatwave that people use water to cool down. It is important people feel they can continue to do that.

"However, people just using water for the sake of it is unacceptable."