San Clemente’s Hard Water, Explained

Where San Clemente’s Water Actually Comes From

San Clemente draws its entire water supply from imported Metropolitan Water District sources — there’s no local groundwater. That imported supply runs at roughly 295 parts per million (about 17.3 grains per gallon), among the hardest water in South Orange County.

Why That Matters for Your Windows

Standard tap water carries dissolved minerals — mostly calcium and magnesium — that stay behind on glass every time the water dries. A hose-and-squeegee clean using regular tap water is, in effect, rinsing salt haze off with water that leaves its own residue behind. That’s why DIY cleaning here often looks worse within days, not better.

Surface Deposits vs. True Etching

Not all hard water marks are the same. Surface mineral deposits — the kind that build up from irrigation overspray hitting ground-floor glass — typically respond well to a professional clean on the first visit. True etching, where calcium has bonded into the glass surface itself over a long period, may not fully reverse. We’ll always look at your glass and tell you honestly what’s achievable before starting.

How Deionized Water Solves This

In-line deionized water treatment strips those dissolved minerals before the water ever touches your glass. We check it with a TDS meter — under 10 parts per million is the standard we run to — so the water doing the cleaning can’t leave a new mineral film behind.

If you’re dealing with visible spotting or staining already, see our Hard Water Spot Removal page for what treatment looks like.

How to Spot Hard Water Marks on Your Windows

Hard water leaves marks that are easy to confuse with ordinary dirt. The difference is that mineral spots stay put: they do not wipe away with glass cleaner, and they often show up as distinct white rings or dots where individual drops dried rather than as an even haze.

• Small white circles or dots that look like dried droplets
• Heavier spotting on the lower part of ground-floor windows
• Marks that return quickly after a DIY clean with a hose
• A chalky feel on the glass when you run a dry fingertip across it

Preventing Mineral Buildup at Home

The single most useful change most homeowners can make is keeping tap water off the glass. That means aiming sprinkler heads away from windows, avoiding hose rinses on glass, and using distilled water for any quick touch-ups. Those small changes slow new buildup, while a periodic clean with deionized water removes what has already dried on. You can read more about the regional water supply from the Metropolitan Water District of Southern California.