Pure De-ionised water. Used to prevent furring and scale formation. For use commonly in steam irons and re-fillable batteries. Also used in window cleaning and due to containing no minerals it will not leave streaks or deposits when dry. Additionally polished and then filtered with a UV lamp the micro-siemen count is typically 5 and always less than 10. (or approximately 10ppm). Protect from daylight for storage. Distilled water has the same properties but it is derived by steam distillation.