Equipment
Deionized water (DI)
Water with minerals removed via ion-exchange resin. Used in pure-water cleaning; identical purity to RO water.
Water that’s been passed through an ion-exchange resin that removes positively- and negatively-charged dissolved minerals. The result is water with TDS near zero — functionally the same as reverse-osmosis water for window cleaning, but produced on-demand from a smaller, truck-mounted filter.
Most professional pure-water window cleaning rigs run a two-stage setup: reverse osmosis first (cheap per gallon, slower) into a tank, then DI polishing (expensive resin, fast) just before it reaches the brush. This gets the water to 0 TDS without burning through DI resin.