Hosepipe bans in parts of drought hit Britain have come into force since midnight. Southern Water, South East Water, Thames Water, Anglian Water, Sutton and East Surrey, Veolia Central and Veolia South East are to enforce restrictions.
Water companies across England and Wales leaked more than 3.3 billion litres of water a day in 2010/11, according to Ofwat, the economic regulator of the water and sewerage industry.
The Environment Agency has urged companies to do more to tackle leakage rates.
Anglican and Southern were among the companies to fail to meet their water leakage targets last year.
Richard Aylard, Thames Water sustainability director, defended his company:
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.