San Diego's imported supply runs 209 to 284 mg/L hard, so irrigation overspray etches glass, and salt aerosol coats homes from Pacific Beach to Point Loma.
San Diego's imported water is very hard to extremely hard, so wherever irrigation reaches the same panes it etches glass instead of just spotting it; a filtered or pure-water final rinse is part of the job. Homes near the coast also collect salt spray, and May to October is the dependable window. Rinse treatment and distance from the coast set the price: a single-story exterior typically runs $330 to $580.
Whichever of the city's two published figures is used, this is very hard water — and at that level the supply damages glass rather than merely marking it, wherever irrigation reaches the same panes repeatedly. A filtered final rinse is the cost of doing the job here, and the practical question is not whether to treat the rinse water but which plant's water a given route is working with.
Figures by plant, as reported.
| Hardness | 209–284 mg/L as CaCO₃ Very hard — plant averages of 231 to 247 ppm (13.5 to 14.4 grains) in the report tables, against the city's customer guidance of about 16 grains, 276 ppm, ranging 272 to 284, as published by City of San Diego Public Utilities Department (imported supply via San Diego County Water Authority). |
|---|---|
| pH | 7.4–9 |
| Alkalinity | 46–155 mg/L as CaCO₃ |
| Corrosion index | Langelier index +0.2 to +1 |
| Sodium | 47.8–136 mg/L |
| Chloride | 59–204 mg/L |
| Total dissolved solids | 105–634 mg/L |
| Disinfectant | chloramine |
| Source and treatment | About eighty-five percent imported Colorado River and State Water Project water via the San Diego County Water Authority, blended with local supply in different ratios at the Alvarado, Miramar and Otay plants · Permanganate and powdered activated carbon for taste and odour, coagulation, rapid mix, sedimentation and rapid sand filtration, chlorination with chloramines as the residual, and pH adjustment for corrosion control · No softening step. |
Not in the report: iron and manganese.
SOURCE · City of San Diego 2025 Annual Drinking Water Quality Report, secondary-standards and other-parameters tables, read with the department's 2025 Additional Characteristics sheet and its non-detected parameters list (sandiego.gov) · How we source these numbers
Two independent clocks run here. Coastal frontage rebuilds a salt film continuously and needs a short year-round cycle; irrigated elevations anywhere in the city accumulate mineral on their own schedule regardless of how dirty the glass looks. The marine layer sets the working hours from May to July rather than the interval, pushing coastal starts later in the morning.
CALIFORNIA SEASON BY SEASON →San Diego publishes hardness twice and the two figures disagree. Its Water Quality page tells customers to expect about 16 grains per gallon — 276 ppm, ranging 272 to 284 — while its own report tables give plant averages of 231 to 247 ppm, or 13.5 to 14.4 grains. Either way this is very hard water, and no conventional plant removes it. Coastal salt and a persistent marine layer define the rest of the operating reality.
The city publishes hardness per treatment plant, not citywide: Alvarado averaging 231 ppm across a 209 to 245 range, Miramar 241 across 217 to 269, and Otay 234 across 217 to 257, with the Metropolitan Skinner plant supply at 247. In grains that is 13.5, 14.1, 13.7 and 14.4 — very hard at every plant and in every range.
Separately, the city's own Water Quality page tells customers that San Diego water typically averages about 16 grains per gallon or 276 ppm and can range from 16 to 18 grains, 272 to 284 ppm, depending on demand and where in the city they live. That sits above its own per-plant tables, so the utility's customer guidance and its report data do not match — a reason to treat any single San Diego figure as approximate.
The department explains the variation itself: because local and imported water are blended in different ratios, hardness varies between treatment plants. Miramar has run on imported water alone, Otay primarily on local water, and Alvarado on a mix — so which plant serves an address is what determines the mineral load it receives.
Roughly eighty-five percent of the supply is imported Colorado River and State Water Project water. Colorado River water in particular spends hundreds of miles dissolving mineral out of rock before it arrives, and no conventional treatment plant removes hardness or dissolved solids — they pass straight through to the tap.
At this concentration, sprinkler overspray stops being a spotting problem and becomes an etching one. Repeated wet-dry cycles of 230-plus mg/L water on the same lower panes leave permanent damage, so identifying irrigation heads is a genuine part of the job and a filtered or deionised final rinse is baseline rather than an upsell.
Coastal exposure on the western half of the city drives heavy salt aerosol. The band from Pacific Beach south through Point Loma needs a dedicated salt-protocol rinse, and the film is hygroscopic — it softens in the marine layer rather than drying hard, so pressure spreads it and flooding removes it.
Marine layer fog persists through mid-morning from May to July, and it is a scheduling constraint rather than a nuisance. Cleaning before it burns off leaves a humidity film that re-streaks within hours, so the productive window on coastal work starts later than crews from inland markets expect.
Sodium runs around 87 to 93 ppm across the plants, which matters because it means a meaningful share of the evaporative residue here is not carbonate. Salt-type residue redissolves in a thorough rinse where true scale needs acid, and the two often arrive on the same pane in this city.
Rinse-water treatment is a real cost in this market rather than an option. Beyond it, distance from the coast drives frequency, the marine layer compresses the usable morning, and restoration on etched glass prices separately from cleaning. La Jolla and Gaslamp both price on appearance standards and short intervals rather than on pane count.
A homeowner can wash glass in San Diego. What they cannot easily do is prevent the two forms of permanent damage: overspray etching, which is cumulative and invisible until it is irreversible, and blown sand on beach-adjacent panes, which scratches the moment anyone wipes rather than floods. The professional value here is diagnostic and preventive more than it is cleaning.
OPEN COST ESTIMATOR →2025 annual mean at the San Diego - Kearny Villa Rd. monitor, 6125A Kearny Villa RD., SAN Diego, 3.6 km north of the city (EPA site 06-073-1016).
Largest air release: General Dynamics (NASSCO), 2798 Harbor DR (transportation equipment), inside the city limits, 127,979 lb in 2024.
San Diego's permanent water rules ban runoff onto walkways, streets and neighbouring property, and allow washing paved areas only with a power washer or a hose with a shut-off nozzle, with the water collected before it reaches a storm drain. Rinse glass with a trigger nozzle and keep the run-off on site.
City of San Diego Public Utilities, Permanent Mandatory Water Restrictions · checked September 2026
San Diego's code makes it illegal to let polluted wash water from pressure washing or hosing down outdoor surfaces, buildings and windows included, reach the storm drain system, with penalties of up to $10,000 a day. With the owner's permission it can go onto landscaping if nothing runs off, or into the site's own sewer through a sink, toilet or cleanout.
City of San Diego Storm Water Division, Pressure Washing fact sheet · City of San Diego, pressure washing and surface cleaning guide for mobile businesses · San Diego Municipal Code §43.0304 and §43.0305: illicit and allowed discharges · checked September 2026
On a designated historical resource, or a building in one of San Diego's historical districts, window work falls under the city's Historical Resources Regulations. Ordinary repair that keeps the windows' type and style, in line with the Secretary of the Interior's Standards, needs only a construction permit; changes that don't qualify need a Neighborhood or Site Development Permit.
San Diego Municipal Code, Historical Resources Regulations (§143.0210 and §143.0220) · checked September 2026
The Pacific coast from San Diego to Eureka sees salt aerosol year-round, heaviest during winter storm season. The Marin headlands, the San Francisco Sunset, the Big Sur coast, and the Malibu beach properties are the heaviest-deposition areas. Salt corrodes aluminum sash hardware over time.
The Bay Area summer fog produces sustained morning condensation on east-facing exposures that redeposits atmospheric particulate as a thin film. Standard cleaning protocols work; the consideration is the cleaning cadence — coastal SF and the Marin shoreline want more frequent service than inland equivalents.
San Diego runs on City of San Diego Public Utilities Department (imported supply via San Diego County Water Authority) a mixed surface-and-groundwater blend at a published 209–284 mg/L (CaCO₃) — very hard — plant averages of 231 to 247 ppm (13.5 to 14.4 grains) in the report tables, against the city's customer guidance of about 16 grains, 276 ppm, ranging 272 to 284.
Residential window cleaning in San Diego typically runs $11–17 per pane or $330–580 for a standard single-story exterior. Rinse-water treatment is a real cost in this market rather than an option.
San Diego's drier, frost-free months are May to October, by NOAA's 1991–2020 normals for the San Diego Montgomery Field station, where February brings the most rain. The calendar on this page marks May (after the February 11 bloom). Frost nights essentially never come here.
Not as the final rinse: City of San Diego Public Utilities Department (imported supply via San Diego County Water Authority) publishes dissolved solids of 105–634 mg/L, enough to spot as it dries, so finish with pure water. It draws on about eighty-five percent imported Colorado River and State Water Project water.
In San Diego the dominant residue patterns include irrigation overspray etching from very hard imported supply and coastal salt aerosol from pacific beach through point loma. Two independent clocks run here.
A homeowner can wash glass in San Diego. What they cannot easily do is prevent the two forms of permanent damage: overspray etching, which is cumulative and invisible until it is irreversible, and blown sand on beach-adjacent panes, which scratches the moment anyone wipes rather than floods. The professional value here is diagnostic and preventive more than it is cleaning.
Dense pre-1920 commercial stock with substantial restaurant storefront glass and nightly cleaning common. Appearance-driven demand on very short intervals. La Jolla and North Park have their own housing stock and glazing as well.
Just over the California line