2026 Rankings

Least Reliable Water Systems in California — 2026

Last updated: April 13, 2026

2,630 ZIP codes ranked by Reliability Score #1: ZIP 91901 (Alpine, CA) - 10/100
Lead Violations Lowest Score Safest Flood Risk Energy Cost Radon PFAS Reliability EJ Index Homebuyer Risk CO & Gas Safest Gas Remediation Burden Unresolved Violations (by Utility) Water Equity (by Utility)

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 91903 Alpine CA 10/100 69/100
3 91931 Guatay CA 10/100 33/100
4 91963 Potrero CA 10/100 55/100
5 91990 Potrero CA 10/100 55/100
6 93240 Lake Isabella CA 10/100 59/100
7 93532 Lake Hughes CA 10/100 53/100
8 93643 North Fork CA 10/100 50/100
9 93644 Oakhurst CA 10/100 57/100
10 93669 Wishon CA 10/100 35/100
11 94556 Moraga CA 10/100 66/100
12 94570 Moraga CA 10/100 45/100
13 94575 Moraga CA 10/100 45/100
14 94582 San Ramon CA 10/100 50/100
15 94583 San Ramon CA 10/100 53/100
16 95231 French Camp CA 10/100 62/100
17 92266 Palo Verde CA 13/100 80/100
18 91935 Jamul CA 15/100 69/100
19 91962 Pine Valley CA 15/100 45/100
20 92311 Barstow CA 15/100 45/100
21 92312 Barstow CA 15/100 39/100
22 92327 Daggett CA 15/100 17/100
23 92338 Ludlow CA 15/100 50/100
24 93247 Lindsay CA 15/100 28/100
25 93267 Strathmore CA 15/100 39/100
26 93283 Weldon CA 15/100 55/100
27 93426 Bradley CA 15/100 69/100
28 93446 Paso Robles CA 15/100 51/100
29 93447 Paso Robles CA 15/100 48/100
30 93534 Lancaster CA 15/100 48/100
31 93535 Lancaster CA 15/100 43/100
32 93536 Lancaster CA 15/100 43/100
33 93539 Lancaster CA 15/100 36/100
34 93584 Lancaster CA 15/100 36/100
35 93586 Lancaster CA 15/100 36/100
36 93615 Cutler CA 15/100 55/100
37 93666 Sultana CA 15/100 64/100
38 93926 Gonzales CA 15/100 53/100
39 94101 San Francisco CA 15/100 53/100
40 94102 San Francisco CA 15/100 59/100
41 94103 San Francisco CA 15/100 59/100
42 94104 San Francisco CA 15/100 59/100
43 94105 San Francisco CA 15/100 59/100
44 94107 San Francisco CA 15/100 59/100
45 94108 San Francisco CA 15/100 59/100
46 94109 San Francisco CA 15/100 59/100
47 94110 San Francisco CA 15/100 59/100
48 94111 San Francisco CA 15/100 54/100
49 94112 San Francisco CA 15/100 54/100
50 94114 San Francisco CA 15/100 59/100
51 94115 San Francisco CA 15/100 59/100
52 94116 San Francisco CA 15/100 54/100
53 94117 San Francisco CA 15/100 53/100
54 94118 San Francisco CA 15/100 59/100
55 94119 San Francisco CA 15/100 53/100
56 94120 San Francisco CA 15/100 59/100
57 94121 San Francisco CA 15/100 59/100
58 94122 San Francisco CA 15/100 59/100
59 94123 San Francisco CA 15/100 59/100
60 94124 San Francisco CA 15/100 59/100
61 94125 San Francisco CA 15/100 53/100
62 94126 San Francisco CA 15/100 53/100
63 94127 San Francisco CA 15/100 59/100
64 94128 San Francisco CA 15/100 53/100
65 94129 San Francisco CA 15/100 53/100
66 94130 San Francisco CA 15/100 53/100
67 94131 San Francisco CA 15/100 59/100
68 94132 San Francisco CA 15/100 59/100
69 94133 San Francisco CA 15/100 59/100
70 94134 San Francisco CA 15/100 53/100
71 94136 San Francisco CA 15/100 53/100
72 94137 San Francisco CA 15/100 53/100
73 94139 San Francisco CA 15/100 53/100
74 94140 San Francisco CA 15/100 53/100
75 94141 San Francisco CA 15/100 53/100
76 94142 San Francisco CA 15/100 53/100
77 94143 San Francisco CA 15/100 53/100
78 94144 San Francisco CA 15/100 53/100
79 94145 San Francisco CA 15/100 53/100
80 94146 San Francisco CA 15/100 53/100
81 94147 San Francisco CA 15/100 53/100
82 94150 San Francisco CA 15/100 53/100
83 94151 San Francisco CA 15/100 53/100
84 94153 San Francisco CA 15/100 53/100
85 94154 San Francisco CA 15/100 53/100
86 94156 San Francisco CA 15/100 53/100
87 94158 San Francisco CA 15/100 53/100
88 94159 San Francisco CA 15/100 53/100
89 94160 San Francisco CA 15/100 53/100
90 94161 San Francisco CA 15/100 53/100
91 94162 San Francisco CA 15/100 53/100
92 94163 San Francisco CA 15/100 53/100
93 94164 San Francisco CA 15/100 53/100
94 94171 San Francisco CA 15/100 53/100
95 94172 San Francisco CA 15/100 53/100
96 94175 San Francisco CA 15/100 53/100
97 94177 San Francisco CA 15/100 53/100
98 94188 San Francisco CA 15/100 53/100
99 94515 Calistoga CA 15/100 70/100
100 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.

Explore More Rankings

How this ranking is calculated, data sources, and limitations: Rankings Methodology →

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Disclaimer: Rankings are based on EPA, FEMA, and federal agency data. They reflect historical patterns and risk indicators, not necessarily current conditions. For the most current information, contact your local water utility or request a Consumer Confidence Report.

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