Put simply Pure water is a process in which tap water has been filtered through a purification system, to remove all the natural minerals. The reason why this vital step is taken is to ensure a clean streak free finish once the pure water dries on your windows.
Pure water is used for window cleaning purposes as opposed to tap water due to the absence of minerals in which tap water contains. Unlike tap water, pure water does not contain calcium, magnesium and other minerals which would leave hard water stains on your windows.
Steps To Make Pure Water