How does San Dimas's water compare to the national average?

The USA national average is 151 mg/L. San Dimas (≈ 120–179 mg/L) is 1 mg/L softer than average.

San Dimas Water Hardness & Quality Report (2026)

Water Hardness

hard

~120–179 mg/L

Hard

estimated · not lab-verified

Source

reservoir

pH Level

8.2

neutral = 7.0

Lead

0.008 mg/L

✓ Below action level

TDS

540.5 mg/L

Est. Daily Cost

$0.40

energy & soap waste

Source: See methodology section below · Updated 2026

hard~120–179 mg/LHard · est.

0–60

mg/L

Soft

61–120

mg/L

Moderately Hard

121–180

mg/L

Hard

180+

mg/L

Very Hard

Appliance Damage Report

In San Dimas, your appliances are currently losing 20% efficiency due to mineral buildup.

Appliance	In San Dimas	Soft Water City	Efficiency Loss
Kettle	6.8 yrs	8.5 yrs	-20%
Washing Machine	9.6 yrs	12 yrs	-20%
Water Heater	12 yrs	15 yrs	-20%

Regional Water Comparison

How San Dimas compares to its nearest neighbours

City	Hardness	PFAS (ppt)	Risk	Source
▶ San Dimas, California	≈ 120–179 mg/L	4.5 ppt	🟠 Hard	reservoir
La Verne, California	≈ 180+ mg/L	0 ppt	🔴 Very Hard	reservoir
Glendora, California	≈ 180+ mg/L	0 ppt	🔴 Very Hard	reservoir
Pomona, California	≈ 180+ mg/L	78.7 ppt	🔴 Very Hard	reservoir
Diamond Bar, California	≈ 180+ mg/L	7.3 ppt	🔴 Very Hard	mixed

National Benchmark

How San Dimas compares to the USA average

Benchmark	Hardness	Appliance Risk
▶ San Dimas	≈ 120–179 mg/L	🟠 Moderate
USA National Avg	151 mg/L	🟠 Moderate
Scarsdale Top Rated	0.02 mg/L	🟢 None

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What Makes San Dimas's Water Unique?

Local geology and source profile

Source: ReservoirTDS: 540.5 mg/LpH: 8.2

Golden State Water Company (GSWC) operates the San Dimas Water System, serving approximately 56,336 people across three cities in Los Angeles County, California. The utility sources water from local groundwater extracted from the San Gabriel Valley basin and imported surface water purchased from the Metropolitan Water District (MWD). Treatment occurs via conventional methods including disinfection with chloramines and UV light, plus filtration at facilities processing both groundwater and surface supplies. The utility can be reached at 626-384-5219 or at 534 N. Barranca Avenue, Covina, CA 91723.

The supply originates in the San Gabriel River watershed, spanning the San Gabriel Mountains to the basin lowlands. The primary aquifer is the San Gabriel Valley groundwater basin, recharged by mountain front infiltration and river percolation through Quaternary alluvial fan deposits. Underlying geology includes the Pliocene-Miocene Fernando Formation with calcareous sandstones and shales, alongside limestone and dolomite fragments and evaporites within the alluvium, which dissolve to impart a hard character through elevated calcium and magnesium. Imported MWD water from the Colorado River Aqueduct and State Water Project adds a surface component with similar moderately mineralized traits.

At hard levels, scale buildup accelerates in pipes, water heaters, dishwashers, and washing machines, with hot water appliances suffering 30–50% higher energy use from encrustation. Maintenance involves annual descaling of fixtures, installing scale-inhibiting filters, and flushing heaters; a water softener is recommended for households to prevent spotting on glassware and improve soap efficiency. GSWC-San Dimas reports 3 contaminants above EPA health-based MCLGs per 2026 data, with an overall B+ quality rating; treatment includes conventional filtration, chloramine disinfection, and UV. City-specific Consumer Confidence Reports should be reviewed for the latest contaminant detections, with utility compliance maintained via MWD coordination.

Geology & Source: San Gabriel Valley alluvial basin — Quaternary river deposits over Miocene-Pliocene Fernando Formation; limestone, dolomite, and evaporite fragments dissolve to produce a hard supply; MWD imports add similar mineralization

Other California Water Reports

La Verne

≈ 180+ mg/L

🔴 Very Hard

Glendora

≈ 180+ mg/L

🔴 Very Hard

Pomona

≈ 180+ mg/L

🔴 Very Hard

Diamond Bar

≈ 180+ mg/L

🔴 Very Hard

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Notice an error or missing data? Help us keep this page accurate. If you spot incorrect water hardness, outdated utility info, or missing details, please let us know.

All reports are reviewed by our team. Thank you for supporting data quality!

Frequently Asked Questions

Is San Dimas's water safe to drink?

Yes. San Dimas's water meets all federal safety standards. The hardness is ≈ 120–179 mg/L (Hard), which is safe to drink. High hardness affects appliances and taste, but poses no health risk.

Do I need a water softener in San Dimas?

At ≈ 120–179 mg/L (Hard), San Dimas's water will cause significant limescale on kettles, washing machines, and water heaters. A water softener or descaler is strongly recommended to extend appliance lifespan and reduce energy bills by up to 20%.

How does San Dimas compare to the USA average?

The USA national average is 151 mg/L. San Dimas (≈ 120–179 mg/L) is 1 mg/L below the national average. The softest major city is Scarsdale at just 0.02 mg/L.

Data Sources & Methodology

Water quality data for San Dimas is derived from geographic and geological modelling of the surrounding region. No federal monitoring station data was available for this location.

Estimated

Water Hardness

Modelled estimate based on state-level USGS geological survey data for this region. No direct USGS Water Quality Portal measurement was matched to this city — the value reflects a statistical range calibrated to the state's dominant rock types and typical source water characteristics.

Estimated

Estimated from regional geology and source water characteristics. pH is correlated with water hardness and local bedrock — values may differ from utility-reported figures.

Estimated

TDS — Total Dissolved Solids

Estimated using a derived ratio from water hardness and regional conductance profiles. TDS in natural water correlates strongly with total mineral content including hardness ions.

Measured

PFAS — Perfluoroalkyl and Polyfluoroalkyl Substances

EPA UCMR5 (5th Unregulated Contaminant Monitoring Rule, 2023–2025) — sum of PFAS compounds detected at the public water system serving this city. A value of 0 indicates the system was sampled with no detection above reporting limits.

Modelled

Lead

Modelled estimate based on the EPA Lead and Copper Rule 90th-percentile tap-sample methodology. No publicly available per-city lead dataset with sufficient national coverage exists. Values are a conservative baseline derived from city population tier and infrastructure age — all estimates are maintained below the EPA action level of 0.015 mg/L.

Calculated

Appliance Lifespan

Calculated from water hardness using a linear degradation model. Baseline lifespans represent soft-water performance (kettle: 8.5 yrs, washing machine: 12.0 yrs, water heater: 15.0 yrs). Hard water mineral scale progressively reduces operational life in direct proportion to hardness concentration.