The public are also being encouraged to 'police' their areas and tip-off water companies if they spot neighbours breaking the rules.
The ban has been put in place after the region's driest winter in 20 years.
The county is officially classed as in drought - with the driest months of the year yet to come.
Thames Water, South East Water and Southern Water have all made the use of hosepipes off-limits to the general public.
Householders who persistently break the rules could face a court appearance and fine of £1,000 if they ignore verbal and written warnings.
Head of water resources and environmental at South East Water Lee Dance said the restrictions are 'regrettable, but necessary'.
Chief executive of Thames Water Martin Baggs conceded the restrictions will be unpopular but there was little choice with reserves so low.
"Anyone who wilfully breaches the terms of the water-use bans can be prosecuted," he warned.
"But we would much prefer to get results asking for people's help, understanding and co-operation."
From today hosepipes cannot be used to water gardens, clean cars, water plants, fill fountains and ponds, clean paths, windows, and patios or for any other domestic uses.
The three suppliers say the ban will remain in place until water levels have increased.
The water boards could also apply to Defra for a Drought Order, which would see restrictions issued to businesses, if the situation deteriorates.
Since March 2010 the region has had 35cm less rain than normal. The last year is the second driest 12 months on record. The last hosepipe ban was in 2006.
Under the ban people can still fill water gardens and clean their cars provided they use a watering can or a bucket.
Hosepipe exemptions exist for some commercial users such as car washes and window cleaners. People with 'severe mobility' issues are also allowed to continue using them.
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