Streaking With Pure Water - Decision Tree

Why this matters

Pure water window cleaning eliminates squeegee labor and unlocks high-rise productivity, but a streaking complaint after a pure-water rinse threatens the entire system's reputation with the property manager. Most "streaking with pure water" calls are diagnosed in under ten minutes once the technician walks the decision tree below. The trap is jumping to "the resin is exhausted" before ruling out user error, ambient contamination, and rinse technique. A misdiagnosis costs a $300 resin recharge that does not fix the problem and a return visit that costs more than the original job's margin.

Step 1 - Measure TDS at the brush head, not at the cart

Pure water is defined as 0 ppm total dissolved solids, measured at the point where water leaves the brush jets and contacts the glass. A TDS meter reading at the cart outlet ignores any contamination introduced by the pole hose or the brush itself. Use an in-line TDS meter or pull a sample directly into a small cup at the brush.

• TDS 0 to 10 ppm: water is clean, proceed to Step 2.
• TDS 11 to 50 ppm: minor breakthrough. If you are running a single DI vessel, schedule recharge within five jobs. If running two-stage RO/DI, check the RO membrane reject ratio.
• TDS over 50 ppm: stop and recharge or replace media. Rinsing with water above 50 ppm will leave visible spots on dark glass and will streak on every surface in direct sun.

Step 2 - Inspect the brush for chemical residue

The most common false-positive "pure water failure" is a brush that was used the previous day with traditional cleaning solution and not flushed. Surfactant trapped in the bristles releases during the rinse and leaves a streak pattern. Rinse the brush in clean pure water for 60 seconds before going back up the pole. If streaking stops, log the root cause as brush contamination and add a "flush brush at end of day" item to the closing checklist.

Step 3 - Check the glass surface for pre-existing contamination

Pure water removes water-soluble soils. It does NOT remove silicone overspray, fresh paint, mineral hard-water etching, or aged construction debris that has bonded to the glass. If the streak pattern follows a defined line - especially horizontal lines below window frames - the contamination is on the glass, not in your water. Touch the streaked area with a dry microfiber. If the residue transfers, it is surface contamination. Pure water cannot fix this; the glass requires a traditional clean with a squeegee, possibly with a Cerium Oxide polish for mineral etching.

Step 4 - Evaluate rinse technique

Pure water needs adequate flow and contact time. Insufficient rinse leaves a thin film of dissolved soil that flash-dries into a streak. Diagnostic prompts:

• Flow rate at the brush: target 0.5 to 1.0 gallons per minute per brush for residential, up to 2.0 gpm for first-clean commercial.
• Rinse pattern: rinse from top of frame down to glass bottom, then pull the brush away while still flowing. Do not stop water flow while the brush is on the glass.
• Dwell on heavy soil: scrub with bristles in contact for at least 15 seconds per pane before rinse-off.

If the technician was rationing water (common when running a small backpack tank), the diagnosis is operator technique. Re-train with a flow-meter visualization at the next crew meeting.

Step 5 - Verify hose and pole condition

Garden hoses, RV hoses, and any hose with a copper or brass internal fitting can re-contaminate water that left the cart at 0 ppm. Pure-water hoses should be black food-grade PVC or polyurethane with stainless fittings. If you are using a yellow contractor hose: it is leaching and you will never hold 0 ppm at the brush. Replace with rated pure-water hose. Inspect pole sections for internal corrosion - aluminum pole sections that have been left wet for extended periods grow oxide scale that releases on first flow each morning. Pre-rinse the pole for 60 seconds into a bucket before going to glass.

Step 6 - Confirm the dry-down

Pure water dries clear with no wipe. Wait at least 10 minutes before judging the result - water spotting visible in the first two minutes after rinse is normal and resolves as the film evaporates. If glass is still streaked after 15 minutes of full dry-down in shade, return to Step 1. The TDS meter is the only objective test in this tree; every other step is qualitative.

Decision summary

Walk the tree top-down. Do not skip Step 2 to get to Step 5 because the recharge is more glamorous. The Pareto distribution of root cause across documented service calls: brush contamination 40%, surface contamination 25%, technique 20%, hose contamination 10%, resin exhaustion 5%. Recharge is the last suspect, not the first.

References

• IWCA I-14.1-2001, Window Cleaning Safety Standard, Annex on water-fed pole systems.
• ANSI/ASSP A1264.1-2017, Workplace Walking and Working Surfaces.
• Tucker USA Pole Systems, Operator Manual, Section 4: Water Quality and Filtration.
• Unger Professional, nLite Hydropower Technical Reference, water purification and flow control.
• OSHA 29 CFR 1910.66, Appendix C, requirements for water-fed pole operator training.