Windscreen wiper water may be the cause of a fifth of cases of Legionnaires' Disease in England and Wales, according to the Health Protection Agency.
Legionnaires' Disease is a rare but potentially deadly condition which is caused when the Legionella bacterium is inhaled and causes pneumonia. Stagnant, warm water is the ideal breeding ground for the disease.
The discovery was found after records showed that professional drivers are five times more likely to be infected by the disease.
The Health Protection Agency says that adding screenwash kills the Legionella bacteria.
"This is a bug which lives in the environment and will take advantage of warm water systems that are not cleaned out," said Professor Hugh Pennington, an expert in bacteriology.
"Legionnaires' is rare but it kills people and it's an extremely unpleasant disease. If you can prevent it with something this simple then it's a no brainer really."