Why You Shouldn’t Use Tap Water in a Windshield Washer Reservoir

Using tap water as opposed to windshield washer fluid during warm weather months might seem like an environmentally friendly, cost-saving idea. However, it could put drivers at greater risk for Legionnaires’ disease.

Great Britain’s Health Protection Agency (HPA) says stagnant water in a vehicle’s washer fluid tank, heated by the engine, provides an ideal environment for the development of Legionella bacteria. It could be responsible for 20 percent of cases of Legionnaires’ disease, a potentially fatal respiratory illness.

An HPA study found traces of Legionella bacteria in about one in five cars where water had been used to clean windshields.

After spraying water on a windshield, a driver may be exposed to the bacteria via a vehicle’s ventilation system or through an open driver’s window. The solution for avoiding such exposures is to use windshield washer fluid, not water, in the windshield washer reservoir.

The agency estimates that professional drivers are five times more likely to be infected with Legionnaires’ disease because of the length of time they spend driving in vehicles.

Symptoms of Legionnaires’ disease include fatigue, headache, dry cough, fever and muscle aches. Between 10 and 15 percent of people who get the disease die from it.