Head-to-head water quality
Houston, TX vs San Diego, CA
Side-by-side water quality comparison: Houston (Grade F) vs San Diego (Grade F). Lead, PFAS, violations, and source-water contamination
Score breakdown
Each factor is shown as raw points (out of the maximum). Higher = better.
Factor
Houston
San Diego
Better
Violations subscore / 45
0.0
0.0
Tie
Lead/Copper subscore / 20
16.0
16.0
Tie
Contaminant subscore / 20
2.8
14.7
San Diego
Compliance subscore / 10
5.0
5.0
Tie
Source subscore / 5
4.0
4.0
Tie
Lead & copper at the tap
Lead and Copper Rule (LCR) 90th-percentile readings — the value that 10% of sampled homes exceed.
Factor
Houston
San Diego
Better
Lead 90th-percentile (latest) · EPA action level: 15 µg/L
0.0 µg/L
0.0 µg/L
Tie
Copper 90th-percentile (latest) · EPA action level: 1.3 mg/L
1.5 mg/L
1.4 mg/L
San Diego
PFAS — "forever chemicals"
UCMR 5 testing, 2023–2025. Federal MCLs: PFOA + PFOS = 4 ng/L; HFPO-DA = 10 ng/L.
Factor
Houston
San Diego
Better
PFAS analytes detected
10 of 30
1 of 30
San Diego
PFAS exceeds federal MCL
Yes
No
San Diego
PFAS hazard index · Sum of (max/MCL) across detected analytes; > 1 indicates exceedance
3.42
—
Houston
Violation history
SDWA enforcement actions — fewer is better.
Factor
Houston
San Diego
Better
Violations (last 5 years)
2,071
24
San Diego
Health-based violations (total)
929
43
San Diego
Unresolved violations
3,572
52
San Diego
Other contaminants tested
UCMR rounds 1–4 + UCMR 5 lithium. Maxima where data exists; "—" means not tested.
Factor
Houston
San Diego
Better
Chromium-6 (max)
6.66 µg/L
0.36 µg/L
San Diego
HAA5 (avg)
18.35 µg/L
9.75 µg/L
San Diego
Manganese (max)
158.90 µg/L
8.20 µg/L
San Diego
Strontium (max)
948.00 µg/L
940.00 µg/L
San Diego
1,4-Dioxane (max)
1.15 µg/L
—
Houston
NDMA (max)
43.30 ng/L
2.20 ng/L
San Diego
Vanadium (max)
16.00 µg/L
0.84 µg/L
San Diego
Chlorate (max)
13600.00 µg/L
200.00 µg/L
San Diego
Molybdenum (max)
12.60 µg/L
4.70 µg/L
San Diego
Industrial proximity
Superfund National Priorities List + Toxic Release Inventory facilities within 10 miles of the city centroid.
Factor
Houston
San Diego
Better
Superfund sites within 10 mi
4
0
San Diego
TRI lbs to surface water within 10 mi (2023)
1,981,876
3
San Diego
System size & source
Factor
Houston
San Diego
Population served
5.9M
1.4M
—
Water source
Surface water
Surface water
—
Number of water systems
719
9
—
See the full reports
Frequently asked
Which has better water — Houston or San Diego?
San Diego, CA scores higher (39.7 vs 27.8) on WaterVerge's 100-point methodology, earning a Grade F compared to Houston's Grade F. The score combines violation history, lead and copper levels, contaminant testing, monitoring compliance, and source-water type.
How is the WaterVerge water quality score calculated?
The grade combines five subscores: violation history (45 pts, weighted by recency and health-based severity), lead/copper 90th-percentile vs EPA action levels (20 pts), contaminant testing including PFAS, chromium-6, HAA5, NDMA, perchlorate, and Superfund/TRI proximity (20 pts), monitoring compliance (10 pts), and water-source-type risk (5 pts). Full methodology at /about/methodology.
Where does this water quality data come from?
From the EPA's public records: the SDWIS bulk download (violations + system info), UCMR rounds 1–5 (unregulated contaminant testing including PFAS, chromium-6, HAA5, NDMA, perchlorate, vanadium, lithium), the EPA Toxic Release Inventory (industrial polluters), the Superfund National Priorities List, the USGS Powell Domestic-Well Database (private-well chemistry), and the CDC Community Water Fluoridation system. Data is refreshed quarterly.