Last updated: October 2026
Why does deionized water dry without spots on exterior windows?
Deionized water carries no dissolved minerals, so it dries on exterior glass without leaving spots. That is why we rinse exterior panes with water-fed brushes and skip the squeegee outdoors. Interior glass is different. We wash it by hand, with microfiber on the frames and sills.
Spotting is a mineral problem. Tap water leaves calcium and other solids behind when it evaporates, and those solids are the white dots you see on a window after a sprinkler hits it.
Take the minerals out first and nothing is left to dry onto the glass.
What happens on an exterior job
We scrub the pane with a water-fed brush, which loosens the film and carries it off with the rinse. Then the glass is left to dry on its own.
On the coast, that film is mostly salt. In Pacific Beach and Point Loma the salt spray settles on the exterior pane faster than it does inland, so the brush work is the part that matters. Rinsing alone would just move it around.
Inland, in Poway or Scripps Ranch, the problem flips. Sprinkler overspray leaves mineral spotting low on the pane, right where the heads throw water.
Squeegee vs deionized rinse: how they compare
| Question | Squeegee on exterior glass | Deionized rinse and brush |
|---|---|---|
| Leaves mineral spots as it dries | Can, if a wet edge is missed | No, nothing dissolved is left behind |
| Touches the frame and sill | Edge of the blade runs the frame | Brush and rinse only |
| Suits high or sloped reach | Needs a ladder at arm's length | Works from the ground on a pole |
Where we still do it by hand
Interiors are not rinsed. We wash them by hand and use microfiber on the glass, frames, and sills, because water running down an inside wall is a bad idea.
Tracks and screens are separate work. Grit in a track is what scratches glass later, so we detail tracks on their own. Screens hold dust that lands back on clean glass the first time the wind blows, so we do screens in the same visit.
You can read how each step runs on our exterior window cleaning page, or see how it plays out near the water on our Pacific Beach page.
Matthew and Tanner do every job themselves and check every pane before we call it done. If we cleaned your windows in San Diego, a Google review that names the service and your neighborhood helps the next homeowner a lot.
