California — 4th District
119th Congress · 70 ZIP codes · Avg score 79/100 · Grade B · Updated 2026-07-19
Data: EPA SDWIS / Census 119th Congress Last verified: 2026-07-19
ZipCheckup tracks water safety for 70 ZIP codes in California's 4th District: the district earns a grade B (79/100). 96 EPA violations on record, 50 health-based.
Top Contaminants
ZIP Codes in This District
70 ZIP codes tracked in California's 4th District. Showing top 50 by safety score.
| # | ZIP Code | City | Safety Score | Grade | Violations |
|---|---|---|---|---|---|
| 1 | 95406 | Santa Rosa | 99 | A | 1 |
| 2 | 95433 | El Verano | 97 | A | 0 |
| 3 | 94926 | Rohnert Park | 95 | A | 0 |
| 4 | 94927 | Rohnert Park | 95 | A | 0 |
| 5 | 94931 | Cotati | 95 | A | 0 |
| 6 | 95402 | Santa Rosa | 95 | A | 1 |
| 7 | 95409 | Santa Rosa | 95 | A | 1 |
| 8 | 95937 | Dunnigan | 95 | A | 1 |
| 9 | 95617 | Davis | 94 | A | 4 |
| 10 | 95443 | Glenhaven | 93 | A | 0 |
| 11 | 94928 | Rohnert Park | 92 | A | 0 |
| 12 | 94589 | Vallejo | 90 | A | 0 |
| 13 | 95404 | Santa Rosa | 90 | A | 1 |
| 14 | 95405 | Santa Rosa | 90 | A | 1 |
| 15 | 95407 | Santa Rosa | 90 | A | 1 |
| 16 | 95426 | Cobb | 89 | A | 4 (2 health) |
| 17 | 95457 | Lower Lake | 89 | A | 2 |
| 18 | 95452 | Kenwood | 88 | A | 1 |
| 19 | 94503 | American Canyon | 87 | A | 0 |
| 20 | 95627 | Esparto | 87 | A | 0 |
| 21 | 95694 | Winters | 87 | A | 0 |
| 22 | 94508 | Angwin | 86 | A | 4 (4 health) |
| 23 | 95618 | Davis | 86 | A | 4 |
| 24 | 95698 | Zamora | 86 | A | 1 (1 health) |
| 25 | 94571 | Rio Vista | 85 | A | 0 |
| 26 | 95401 | Santa Rosa | 85 | A | 1 |
| 27 | 95422 | Clearlake | 83 | B | 2 (2 health) |
| 28 | 95776 | Woodland | 83 | B | 2 (1 health) |
| 29 | 95442 | Glen Ellen | 82 | B | 0 |
| 30 | 95467 | Hidden Valley Lake | 82 | B | 0 |
| 31 | 95620 | Dixon | 82 | B | 0 |
| 32 | 95485 | Upper Lake | 81 | B | 3 (1 health) |
| 33 | 95616 | Davis | 81 | B | 4 |
| 34 | 95453 | Lakeport | 80 | B | 0 |
| 35 | 95696 | Vacaville | 80 | B | 7 (6 health) |
| 36 | 94599 | Yountville | 79 | B | 3 (1 health) |
| 37 | 95451 | Kelseyville | 78 | B | 0 |
| 38 | 95695 | Woodland | 78 | B | 2 (1 health) |
| 39 | 95464 | Nice | 77 | B | 0 |
| 40 | 94512 | Birds Landing | 73 | B | 0 |
| 41 | 94562 | Oakville | 73 | B | 0 |
| 42 | 94573 | Rutherford | 73 | B | 0 |
| 43 | 95416 | Boyes Hot Springs | 73 | B | 0 |
| 44 | 95435 | Finley | 73 | B | 0 |
| 45 | 95476 | Sonoma | 73 | B | 4 (1 health) |
| 46 | 95606 | Brooks | 73 | B | 0 |
| 47 | 95612 | Clarksburg | 73 | B | 0 |
| 48 | 95637 | Guinda | 73 | B | 0 |
| 49 | 95645 | Knights Landing | 73 | B | 0 |
| 50 | 95653 | Madison | 73 | B | 4 (1 health) |
Overview
California's 4th District encompasses 70 ZIP codes tracked by ZipCheckup. The district's average Home Safety Score is B (79/100).
96 EPA violations have been recorded across this district's water systems. 50 are health-based violations. About 46% of tracked ZIP codes have at least one violation.
Top Contaminants
The most frequently cited water quality issues in this district:
- Stage 2 DBP Rule - 27 violations
- Haloacetic Acids (HAA5) - 19 violations
- Total Trihalomethanes (TTHM) - 18 violations
- Consumer Confidence Report Rule - 17 violations
- Stage 1 DBP Rule - 13 violations
Housing Context
Homes in this district were built on average around 1975 (~51 years old). Older homes may have lead pipes or solder - consider a water filter if your home predates 1986.
Lead Alert: 4 ZIP codes in this district exceed the EPA action level for lead. Consider using a certified lead-removal filter.
Data Sources
- Water quality violations: EPA Safe Drinking Water Information System (SDWIS)
- Congressional district boundaries: U.S. Census Bureau, 119th Congress
- Housing age: U.S. Census Bureau American Community Survey
Updated daily. Data covers 70 ZIP codes in California's 4th District.