If you use straight water, or low level of methyl alcohol, bacterial growth is likely to occur if the washer system is not used on a regular basis. This growth occurs with heating and cooling of the water or liquid. When the washer system is eventually used, the water spray is dispersed onto the windshield resulting in the bacteria being carried in the water droplets which then become airborn and inhaled by the person. This bacteria then grows in the lungs and results in a condition known as Legionnaires Disease. If you would like further information related to these circumstances, a simple Internet search will provide you with further information to these specific circumstances as a result of using only water or low-level anti-bacterial agents. These accounts were especially well documented in the UK. I will not post direct links on this forum as there is an ample amount of scientific information available through the NHS and various media outlets.