07/10/2026
The idea that windshield washer reservoirs could spread Legionnaires' disease emerged in the late 2000s after researchers noticed that professional drivers, especially truck drivers, were developing Legionnaires' disease more often than expected.
A large UK case-control study published in 2010 found that using plain water instead of screenwash in windshield washer reservoirs was associated with a substantially higher risk of infection.
The researchers estimated that up to 20% of sporadic, community-acquired Legionnaires' disease cases in England and Wales could be linked to this exposure. They concluded that regular use of screenwash, which typically contains alcohol and other antimicrobial ingredients, likely reduces the growth of Legionella bacteria in washer reservoirs.
The bacteria can multiply in warm, stagnant water, and when the windshield washers are activated, tiny droplets may be inhaled by the driver. This estimate does not apply to all Legionnaires' disease cases as many are linked to cooling towers, plumbing systems, hot tubs, hospitals, hotels, and other building water systems.
The findings led health agencies in both the UK and the United States to recommend using windshield washer fluid rather than plain water, particularly for people who drive frequently.