Diamond Bar Water Hardness & Quality Report (2026)
Water Hardness
10.8 grains per gallon
Source
mixed
pH Level
8.3
neutral = 7.0
Lead
0.008 mg/L
✓ Below action level
TDS
575.8 mg/L
Est. Daily Cost
$0.49
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
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 Diamond Bar, your appliances are currently losing 25% efficiency due to mineral buildup.
| Appliance | In Diamond Bar | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 3.5 yrs | 8.5 yrs | -59% |
| Washing Machine | 6.8 yrs | 12 yrs | -43% |
| Water Heater | 8.2 yrs | 15 yrs | -45% |
Regional Water Comparison
How Diamond Bar compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Diamond Bar, California | 185 mg/L | 7.3 ppt | 🔴 Very Hard | mixed |
| Walnut, California | 151.5 mg/L | 6.3 ppt | 🟠 Hard | mixed |
| Chino Hills, California | 103 mg/L | 4.9 ppt | 🟡 Moderately Hard | mixed |
| Pomona, California | 178 mg/L | 7.1 ppt | 🟠 Hard | mixed |
| San Dimas, California | 177 mg/L | 7 ppt | 🟠 Hard | mixed |
National Benchmark
How Diamond Bar compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Diamond Bar | 185 mg/L | 🔴 High |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
Bring Badger-quality water to your Diamond Bar home
Shop water softeners on Amazon.com →
What Makes Diamond Bar's Water Unique?
Local geology and source profile
Diamond Bar, California, in east Los Angeles County on the Los Angeles–San Bernardino County line at the foot of the Puente Hills — a suburban Inland Empire gateway community adjacent to Pomona and Chino Hills, known as the 'Gem of the Hills' — draws its municipal water supply from the Puente Basin groundwater and Metropolitan Water District (MWD) imported water via the Walnut Valley Water District (WVWD). Water hardness in Diamond Bar measures 185 mg/L — classified as hard.
Diamond Bar's hard supply reflects the Puente Basin's calcareous alluvial geology. The Puente Basin Groundwater Basin (the Pomona–Diamond Bar Quaternary alluvial basin at the east end of the Puente Hills) receives recharge from the Puente Hills — the Miocene Puente Formation (calcareous marine sandstone and shale of the outer Transverse Ranges), the Pliocene San Pedro Formation (calcareous cobble and sand), and the Quaternary Diamond Bar alluvial fan (calcareous gravel from the Puente Hills and Chino Hills drainage). The Walnut Valley Water District also distributes MWD imported water with a moderate Colorado River–SWP blend for the east LA County area, but the Puente Basin groundwater's calcareous content from the Miocene marine formations dominates at the hard 185 mg/L.
At 185 mg/L, Diamond Bar residents face regular hard water challenges. Scale deposits form on faucet aerators, showerheads, and appliances within weeks — monthly descaling with citric acid solution is standard maintenance. Walnut Valley Water District consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.
Geology & Source: Groundwater from the Puente Basin Groundwater Basin and Metropolitan Water District (MWD) imports via the Walnut Valley Water District (WVWD) — the east Los Angeles County–San Bernardino County line Puente Hills alluvial basin; hard supply at 185 mg/L — reflecting the Puente Basin calcareous alluvial recharge from the Puente Hills calcareous Miocene formation drainage.