The south east of England is now in a state of drought, according to the Department for Environment, Food and Rural Affairs.
The region joins parts of eastern England, which have been drought-afflicted since last summer, with some reservoirs, rivers and groundwater aquifers in the South East well below normal levels after two dry winters.
The state of drought in the region was declared after the Environment Department (Defra) convened a summit of water companies, farmers and wildlife groups today to discuss potential water shortages in England.
Following the summit, Thames Water warned that there was a high chance of water restrictions such as hosepipe bans this summer, unless there was significant rainfall or customers used less water.
Some rivers and groundwater levels are lower than during the drought of 1976.
In the South East, Ardingly reservoir in West Sussex and Bewl in Kent are around two-fifths of their normal levels, according to the Environment Agency.
Southern Water has applied for a drought permit to help refill Bewl reservoir, while late last year South East Water was granted a drought order to help refill Ardingly.
Anglian Water has also been issued with two drought permits to refill two of its reservoirs.
Speaking after today's drought meeting at Defra, Environment Secretary Caroline Spelman said: "Ensuring we have enough water this summer is vitally important, and that is why I called the summit today.
"Drought is already an issue this year with the South East, Anglia and other parts of the UK now officially in drought, and more areas are likely to be affected as we continue to experience a prolonged period of very low rainfall.
"It is not just the responsibility of Government, water companies and businesses to act against drought. We are asking for the help of everyone by urging them to use less water and to start now."
Thames Water's sustainability director Richard Aylard said: "None of us know how much rain we're going to get this year, so to plan for the worst and hope for the best is a very sensible move.
"Much of south-east England already has got a drought situation. The worrying thing is we've had such little rain the groundwater stores that we rely on to keep the rivers flowing are very low.
"Things are going to get worse unless we have significant rainfall over the next couple of months."
A recent survey of Thames Water customers revealed that almost half (45%) thought it was unlikely or very unlikely the region would face a drought this year - but that two-thirds accepted they could save water if there were shortages.
Mr Aylard urged people to think about how much water they use.
He added: "There is a high chance we will need restrictions at some stage this summer unless either we get a lot of rain or fantastic co-operation from customers using less water."
Thames Water says people can save water with simple measures, such as turning off the tap while cleaning their teeth or taking shorter showers, fixing leaks and only washing full loads of laundry.
Caroline Spelman chairs a summit meeting to discuss potential water shortages.
All but dried up: The River Kennet in the south of England, and a tributary of the River Thames
Simon Evans from Thames Water walks on a small muddy patch where the river Kennet usually flows along fields near the village of Lockeridge, just West of Marlborough.