More than half of drivers say they will only wash their vehicles every two months or more in the event of a hosepipe ban, according to a nationwide survey.
The water restrictions have already come into force across parts of the South East and East Anglia.
But windscreen firm Autoglass, which conducted the poll, warns a significant drop in cleaningcould impair good visibility on the roads and jeopardise safety.
Just 29 per cent plan to wash their vehicles fortnightly or more once a ban is enforced, according to the poll.
And four in ten drivers said they could not afford to take their vehicles to a car wash as an alternative to hand washing at home.
Autoglass managing director Matthew Mycock said: “Our advice to motorists is to take extra care of their vehicles, making sure they clean their windscreens on a weekly basis.
“This is particularly important during the summer months, when a combination of strong sunlight and dirty windscreens can cause impaired visibility on the roads.
“The restrictions mean motorists need to be smarter about how they use water to clean their cars, but removing dust and debris from windscreens whenever possible and hand washing will prevent putting road users at risk.”
Motorists in East Anglia are the ones most likely to put off cleaning their vehicle with 69 per cent saying they would delay it for two months or more with those in the South East next on 61 per cent.
Those in the East Midlands are the most determined to scrub their vehicles as often as possible with 16 per cent vowing to do it once a week.