There are two ways to remove TDS from Tap Water for Window Cleaning - De-Ionization (DI) and Reverse Osmosis (RO).
This presentation explains how an RO Filter works to purify water … it is not perfect, and often you will still need to ‘polish’ the RO OUTPUT Water with DI to make it spot-free - but the filtering work it does, is practically free !
There are more explanations on the ‘VIDEOS’ page of www.mylocaltds.com