I was interested to read the letter from your correspondent regarding the illness he picked up from his car's air-con. However, of far greater concern to me is the health hazards that lie within the windscreen washer bottle. This water is normally stored under the bonnet where it is constantly warmed up by the heat from the engine and then allowed to cool. This process encourages all types of nasty bugs to develop, the worst of which is Legionnaire's disease that can be a killer. The golden rules to observe are to always use an additive in the washer bottle, this helps to keep the water fresh and more important, always ensure that the car windows are closed when using the washers to ensure that no water vapour enters the cab. Very few motorists appear to be aware of this hazard but it’s worth taking sensible precautions because the bugs in the washer bottle can present a real danger to health.