More than 40million people have been hit with a hosepipe ban or told to watch their water usage as Britain swelters under its third heatwave this year.Five water companies now have severe restrictions in place – preventing about 11million from using hosepipes to water plants and lawns, wash cars or fill paddling pools.A further 33million are being urged to be 'mindful' of their water usage. This advice often precedes a hosepipe ban.Experts warn that the risk of a drought is increasing as temperatures of more than 35C (95F) were recorded in places such as Derbyshire and Hertfordshire yesterday.Anglian Water's restrictions, which will affect five million residents across the East of England, will come into force today.Dr Geoff Darch, the company's head of planning, said: 'We are now at the point where we need customers to help by hanging up the hosepipe, letting lawns go brown and cars go dirty.'Affinity Water also told 3.8million customers across areas including Bedfordshire, Berkshire and Surrey to control their usage 'immediately', with a full ban coming into force next Friday.Southern Water has also introduced a hosepipe ban, affecting about one million customers across Hampshire and the Isle of Wight. The parched grass of Greenwich Park in south-east London on Friday as the heatwave continued