Out of 2,630 ZIP codes with data in California, these are the lowest-ranked areas for reliability score. See also: National Least Reliable Water Systems in America | All California Rankings
| Statistic | Value |
|---|---|
| ZIP codes ranked | 2,630 |
| Lowest value | 10/100 |
| Median value | 75/100 |
| State | California |
100 Lowest-Ranked ZIP Codes
| Rank | ZIP Code | City | State | Reliability Score | Safety Score |
|---|---|---|---|---|---|
| 1 | 91901 | Alpine | CA | 10/100 | 66/100 |
| 2 | 91931 | Guatay | CA | 10/100 | 33/100 |
| 3 | 91963 | Potrero | CA | 10/100 | 55/100 |
| 4 | 93240 | Lake Isabella | CA | 10/100 | 59/100 |
| 5 | 93532 | Lake Hughes | CA | 10/100 | 53/100 |
| 6 | 93643 | North Fork | CA | 10/100 | 50/100 |
| 7 | 93644 | Oakhurst | CA | 10/100 | 57/100 |
| 8 | 93669 | Wishon | CA | 10/100 | 35/100 |
| 9 | 94556 | Moraga | CA | 10/100 | 66/100 |
| 10 | 94575 | Moraga | CA | 10/100 | 45/100 |
| 11 | 94582 | San Ramon | CA | 10/100 | 50/100 |
| 12 | 94583 | San Ramon | CA | 10/100 | 53/100 |
| 13 | 95231 | French Camp | CA | 10/100 | 62/100 |
| 14 | 92266 | Palo Verde | CA | 13/100 | 80/100 |
| 15 | 91935 | Jamul | CA | 15/100 | 69/100 |
| 16 | 91962 | Pine Valley | CA | 15/100 | 45/100 |
| 17 | 92311 | Barstow | CA | 15/100 | 45/100 |
| 18 | 92327 | Daggett | CA | 15/100 | 17/100 |
| 19 | 93247 | Lindsay | CA | 15/100 | 28/100 |
| 20 | 93267 | Strathmore | CA | 15/100 | 39/100 |
| 21 | 93283 | Weldon | CA | 15/100 | 55/100 |
| 22 | 93426 | Bradley | CA | 15/100 | 69/100 |
| 23 | 93446 | Paso Robles | CA | 15/100 | 51/100 |
| 24 | 93534 | Lancaster | CA | 15/100 | 48/100 |
| 25 | 93535 | Lancaster | CA | 15/100 | 43/100 |
| 26 | 93536 | Lancaster | CA | 15/100 | 43/100 |
| 27 | 93615 | Cutler | CA | 15/100 | 55/100 |
| 28 | 93666 | Sultana | CA | 15/100 | 64/100 |
| 29 | 93926 | Gonzales | CA | 15/100 | 53/100 |
| 30 | 94102 | San Francisco | CA | 15/100 | 59/100 |
| 31 | 94103 | San Francisco | CA | 15/100 | 59/100 |
| 32 | 94104 | San Francisco | CA | 15/100 | 59/100 |
| 33 | 94105 | San Francisco | CA | 15/100 | 59/100 |
| 34 | 94107 | San Francisco | CA | 15/100 | 59/100 |
| 35 | 94108 | San Francisco | CA | 15/100 | 59/100 |
| 36 | 94109 | San Francisco | CA | 15/100 | 59/100 |
| 37 | 94110 | San Francisco | CA | 15/100 | 59/100 |
| 38 | 94111 | San Francisco | CA | 15/100 | 54/100 |
| 39 | 94112 | San Francisco | CA | 15/100 | 54/100 |
| 40 | 94114 | San Francisco | CA | 15/100 | 59/100 |
| 41 | 94115 | San Francisco | CA | 15/100 | 59/100 |
| 42 | 94116 | San Francisco | CA | 15/100 | 54/100 |
| 43 | 94117 | San Francisco | CA | 15/100 | 53/100 |
| 44 | 94118 | San Francisco | CA | 15/100 | 59/100 |
| 45 | 94121 | San Francisco | CA | 15/100 | 59/100 |
| 46 | 94122 | San Francisco | CA | 15/100 | 59/100 |
| 47 | 94123 | San Francisco | CA | 15/100 | 59/100 |
| 48 | 94124 | San Francisco | CA | 15/100 | 59/100 |
| 49 | 94127 | San Francisco | CA | 15/100 | 59/100 |
| 50 | 94129 | San Francisco | CA | 15/100 | 53/100 |
| 51 | 94130 | San Francisco | CA | 15/100 | 53/100 |
| 52 | 94131 | San Francisco | CA | 15/100 | 59/100 |
| 53 | 94132 | San Francisco | CA | 15/100 | 59/100 |
| 54 | 94133 | San Francisco | CA | 15/100 | 59/100 |
| 55 | 94134 | San Francisco | CA | 15/100 | 53/100 |
| 56 | 94158 | San Francisco | CA | 15/100 | 53/100 |
| 57 | 94515 | Calistoga | CA | 15/100 | 70/100 |
| 58 | 95012 | Castroville | CA | 15/100 | 53/100 |
Methodology
Water system reliability scores (0-100) combine violation frequency, violation recency, resolution rate, and system size. Systems with repeated health-based violations and unresolved issues score lowest. The reliability score focuses specifically on the water utility performance, distinct from the broader Home Safety Score.
Data sources: EPA Safe Drinking Water Information System (SDWIS), FEMA National Flood Insurance Program, EPA radon zone maps, EIA electricity rates, and Consumer Confidence Reports. Last updated: 2026-04-13.
Frequently Asked Questions
What does a low water reliability score mean?
A low reliability score (below 50) indicates a water system with frequent violations, poor resolution rates, or recurring compliance issues. These systems may have aging infrastructure, inadequate treatment, or management challenges.
How is reliability different from safety score?
The reliability score focuses specifically on the water utility performance (violations, resolution, compliance). The Home Safety Score is broader, also including lead risk, radon, and flood data. A ZIP code can have a reliable water system but still have high radon or flood risk.
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