David Cameron insists it is vital that hosepipe bans in the south east are "obeyed".
"We've had not just dry periods but particularly dry winters for the last few years - so that's why there are hosepipe bans."
Millions of homeowners have been banned from using hosepipes from today as drought grips parts of the country.
Deep underground, the drying-up boreholes of East Sussex show the extent of the UK's drought problem.
20 million people across the south and east of England will be hit by hosepipe bans that have come into effect since midnight.