One would think that the most likely source for Legionnaire’s disease for passengers would be the liquid condensation that can accumulate in the AC system.
Since washer fluid stays contained until it reaches outside of the car I would agree with you that it more than likely would be in the car’s AC system.
http://en.wikipedia.org/wiki/Legionnaires%27_disease
Legionnaires’ disease is transmitted by inhalation of aerosolized water and/or soil contaminated with the bacteria. It is not airborne and it is not transmitted from person-to-person. Sources where temperatures allow the bacteria to thrive include hot-water tanks, cooling towers and evaporative condensers of large air-conditioning systems, such as those commonly found in hotels and large office buildings. Though the first known outbreak was in Philadelphia, Pennsylvania, cases of legionellosis have occurred throughout the world.[5]
Legionella pneumophila thrives in aquatic systems where it is established within amoeba in a symbiotic relationship. In the built environment, central air conditioning systems in office buildings, hotels, and hospitals are sources of contaminated water.[13] Other places it can dwell include cooling towers used in industrial cooling systems as well as evaporative coolers, nebulizers, humidifiers, whirlpool spas, hot water systems, showers, windshield washers, fountains, room-air humidifiers, ice making machines, and misting systems typically found in grocery store produce sections.[14][15]
Potential sources of contaminated water include cooling towers (some 40% to 60% of ones tested[16]) used in industrial cooling water systems as well as in large central air conditioning systems, evaporative coolers, nebulizers, humidifiers, whirlpool spas, hot water systems, showers, windshield washers,[15] architectural fountains, room-air humidifiers, ice making machines, misting equipment, and similar disseminators that draw upon a public water supply.
Yes. One would.
But most people would rather drive with a dirty windshield than without air conditioning.
;-)