Contaminated screen wash water is a widespread problem and often produces unpleasant odours. All water contains some micro-organisms that will increase to unhealthy levels in water stored over long periods. Bacteria that cause problems, attach to inner submerged surfaces including plastic tubing and produce a slimy matrix protective biofilm. Many organisms are contained within a biofilm, including legionella bacteria that can be infectious when sprayed onto a windscreen because they can be drawn into the car via the vent beneath the windscreen. Biofilms are notoriously difficult to remove, particularly from plastic tubing, and most disinfectants are unable to penetrate biofilms and kill the bacteria. If biofilms are removed from areas partly accessible by brushing or high pressure, immediately afterwards they will quickly reform and repeat the process again.

A specially formulated disinfectant, PuriSol which is based on chlorine dioxide, should be added to the screen wash water in the reservoir which will then remove all biofilms in the system, killing the bacteria, prevent further growth and eradicate odours. Three capfuls of PuriSol should be added to the screen wash water each time it is refilled. The reservoir should only be filled with drinking water using a jug or container, not a garden hose, which is a breeding ground for micro-organisms. Chlorine Dioxide has been proven to be hugely effective in the removal of biofilm biomass. PURISOL is available from most caravan accessory shops.