What Is Deionized Water Window Cleaning, and Why Does It Dry Spot-Free?

Deionized water is ordinary water with the minerals removed

Deionized water is tap water with the dissolved minerals taken out of it. Municipal and well water carries calcium, magnesium, sodium, silica, iron and manganese in solution, measured as total dissolved solids, or TDS, in parts per million. A TDS meter is the entire test: dip the probe, read the number. Most Treasure Valley tap water we meter at the spigot reads somewhere between roughly 150 and 400 ppm, and private wells on the valley floor read higher than that. Deionized water reads 0 ppm at our brush head, and anything above 10 ppm means the resin needs changing. Nothing else about the water changes. It is the same H2O at the same temperature and the same pressure. The only difference is that there is no longer anything dissolved in it that can be stranded on a pane of glass when it evaporates.

How ion-exchange resin strips the minerals out

Ion-exchange resin removes minerals by trading them for the ingredients of water itself. The resin is a bed of small plastic beads, and it comes in two types. Cation resin holds hydrogen ions and swaps them for positively charged minerals in the stream: calcium, magnesium, sodium, iron. Anion resin holds hydroxide ions and swaps them for negatively charged ones: bicarbonate, chloride, sulfate, silica. The hydrogen and hydroxide released in the trade combine into more water. A mixed-bed tank does both jobs in one vessel, which is what most window cleaning trucks run, ours included. Resin is not a filter and strains nothing out mechanically; it binds the minerals chemically and holds onto them. When every exchange site is occupied the resin is spent, output TDS climbs off zero, and the tank has to be recharged or refilled. Hard water in equals resin burned.

Why pure water dries spot-free, and why no soap is used

Water spots are not water. They are the minerals the water left behind when it evaporated. Rinse a window with 250 ppm tap water and every drop deposits its share of calcium and silica as it dries, so a hundred drops make a hundred small white rings. Rinse that same window with 0 ppm water and the drop evaporates into nothing, because there is nothing in it to strand on the glass. That is the whole mechanism, and it is why a pure-water clean is finished wet and left to sheet-dry rather than squeegeed and towelled. Pure water also carries no soap, which matters more than it sounds. Surfactant film left in the corners of a pane holds dust and shows as haze in low-angle sun within a week or two. No soap goes on the glass, so no soap has to come back off.

What the work actually looks like on a house

A pure-water exterior clean is done from the ground with a water-fed pole. Purified water runs from the tank through a hose, up a carbon-fiber pole, to a brush head with jets on either side of the bristles, at roughly 1 to 2 gallons per minute. The technician scrubs the frame and the glass under flowing water, rinses top to bottom, and walks away. No squeegee, no towel, no ladder on most homes. Working poles reach about 25 to 45 feet, which covers the majority of two- and three-story Treasure Valley houses from ground level. Glass temperature sets the schedule more than air temperature does: above roughly 100 degrees on a sun-facing pane the rinse flash-dries before it can sheet off, so south and west elevations get worked in the morning in July and August. Below freezing, exterior work waits for a thaw.

Why hard Treasure Valley water makes this method worth it

Local water hardness is the reason this method earns its keep in the Treasure Valley, and also the reason it costs more to run here. Valley ground and canal water is mineral-heavy, so a plain hose rinse spots glass almost immediately, and pressurized irrigation overspray from April through mid-October leaves a gritty film on lower panes all summer. That same hardness is what burns through ion-exchange resin. The higher the incoming TDS, the fewer gallons a tank produces before it is exhausted, so a company running pure water in Meridian goes through resin considerably faster than one running it in a soft-water region. Reflekt uses 100% deionized water and no soap on every exterior job anyway, because the alternative is a soaped-and-squeegeed pane that picks up dust in its corners and shows every drip line the first time it rains.

What deionized water will not do

Deionized water does not remove hard water stains that have already etched into the glass. Once mineral deposits have sat through enough heat and sun cycles they bond to the silica surface, and pure water runs right over them. Removing that takes a separate hard water stain treatment, an acidic gel or a cerium oxide polish worked by hand, pane by pane, and on badly etched glass the honest answer is that some scarring is permanent and no product brings it back. Pure water also will not touch paint overspray, stucco splatter, construction adhesive, silicone or tape residue; those get scraped and solvent-treated. It does not fix a fogged double-pane window either, because that haze is condensation sealed between two panes of glass where no cleaning method reaches. A fogged unit is a glass replacement, not a cleaning.

When pure water is the wrong tool, and what Reflekt charges

Pure water is an exterior method, so it is never the whole job. Interior glass is still cleaned by hand with a squeegee and towel, because nobody wants a gallon a minute running down a wall, and indoor glass faces no rain or wind to dirty it in the first place. Two other cases argue for setting expectations up front. A first pure-water clean on a house that has been soaped for years can still spot slightly on the first visit or two while old residue bleeds out of the frames and gaskets. And single-pane wood sash with cracked or missing glazing putty should be repaired before it takes a flowing-water rinse. Reflekt prices window cleaning from $199 by pane count, screens at $50, gutters from $199, with monthly and quarterly memberships and no contract.