This ties directly to our deionized water cleaning method — see our full deionized pure water window washing guide for complete pricing, scope, and scheduling.

The Single Biggest Quality Variable Is Water — Not Technique

Most people assume window cleaning quality is about technique. Technique matters. But the water source used for exterior cleaning matters more. A mediocre technician with deionized water produces better spot-free results than an expert with tap water — because water chemistry determines what’s left on glass when it evaporates, and what’s left is what the client sees.

What Tap Water Leaves on Portland Glass

Portland’s Bull Run reservoir water is clean by municipal standards — but still contains dissolved calcium, magnesium, and silica at 20–50 ppm. When tap water evaporates on glass, these minerals remain as a thin deposit. Single cycles are invisible. Dozens of repeated wetting-and-drying cycles (the cleaning process, then rain, then drying) build visible white or hazy deposits. This is where “spots” come from.

What Soap Adds to the Problem

Professional soap reduces surface tension and lifts contamination — both useful. But soap also leaves a thin organic film when it evaporates, even when fully rinsed. This film is why soap-cleaned Portland windows re-soil in 2–3 weeks. Pollen adheres to the soap residue surface. Deionized-cleaned windows stay clean 4–6 weeks under the same conditions because there’s no adhesion substrate left on the glass.

Portland City Code 17.39 — The Legal Dimension

For commercial window washing, the water choice is also a compliance issue. Portland City Code 17.39 prohibits chemical discharge into the stormwater system from exterior cleaning. Soap-based commercial window washing technically violates this code. Deionized water cleaning produces zero chemical discharge — only water, with less dissolved mineral content than Portland’s tap water. This is why Perfect Pays PDX’s system is a genuine commercial advantage.

What to Ask Any Portland Window Cleaner

• “Do you use deionized water?” — ask for the TDS output. Professional systems produce 0–5 ppm. Consumer portable units produce 20–50 ppm.
• “Do you use soap?” — if yes, ask whether they rinse with deionized water afterward.
• “What’s your TDS output?” — below 10 ppm is the professional threshold.