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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Side-by-side comparison of tap water quality
| Metric | San Francisco | Los Angeles | Better |
|---|---|---|---|
| Overall Score | 86/100 | 73/100 | San Francisco |
| Grade | A- | B- | - |
| Contaminants Tested | 9 | 8 | - |
| Above EPA Limits | 0 | 0 | Tie |
| EPA Violations (Unresolved) | 0 | 0 | Tie |
| Water Source | groundwater | surface | - |
| Population Served | 876,036 | 3,899,009 | - |
Side-by-side contaminant levels as percentage of EPA limits
| Contaminant | San Francisco | Los Angeles | EPA Limit | Lower Level |
|---|---|---|---|---|
| Total Trihalomethanes | 33.45 ug/L (41.8% of limit) | 26.07 ug/L (32.6% of limit) | 80.00 ug/L | Los Angeles |
| Mercury | 0.0006 mg/L (29.3% of limit) | 0.0004 mg/L (17.9% of limit) | 0.0020 mg/L | Los Angeles |
| Lead | 0.0043 mg/L (28.7% of limit) | Not tested | 0.015 mg/L | N/A |
| Chromium | 0.0016 mg/L (1.6% of limit) | 0.028 mg/L (28.4% of limit) | 0.100 mg/L | San Francisco |
| Arsenic | 0.0005 mg/L (4.7% of limit) | 0.0025 mg/L (25.4% of limit) | 0.010 mg/L | San Francisco |
| Fluoride | 0.957 mg/L (23.9% of limit) | Not tested | 4.00 mg/L | N/A |
| Copper | 0.229 mg/L (17.6% of limit) | 0.013 mg/L (1.0% of limit) | 1.30 mg/L | Los Angeles |
| Nitrite | 0.152 mg/L (15.2% of limit) | 0.144 mg/L (14.4% of limit) | 1.00 mg/L | Los Angeles |
| Haloacetic Acids | Not tested | 7.91 ug/L (13.2% of limit) | 60.00 ug/L | N/A |
| Nitrate | 1.31 mg/L (13.1% of limit) | 0.534 mg/L (5.3% of limit) | 10.00 mg/L | Los Angeles |
Based on contaminants detected in each city
San Francisco's water quality is good. An activated carbon filter would improve taste and provide extra protection.
Consider an activated carbon filter or pitcher filter to reduce chlorine and improve taste.
San Francisco outperforms Los Angeles in overall water quality, scoring 86/100 compared to 73/100. This 13-point difference reflects meaningful distinctions in contaminant levels, EPA compliance history, and water infrastructure quality. The gap is driven by differences in source water protection, treatment technology, distribution system age, and the regulatory track record of each city's water utility. Residents in both cities should understand what these scores mean for their daily water use and health.
San Francisco draws from groundwater sources serving approximately 876,036 people, while Los Angeles relies on surface sources serving about 3,899,009 residents. The type of source water significantly affects the contaminants that must be addressed during treatment. Surface water sources such as rivers and reservoirs are more susceptible to agricultural runoff, microbial contamination, and seasonal turbidity, while groundwater sources may contain naturally occurring minerals like arsenic, radium, or fluoride depending on local geology. Both cities treat their water to meet EPA standards under the Safe Drinking Water Act, but the specific treatment processes and their effectiveness vary based on the challenges posed by each source.
Water quality scores are based on EPA SDWIS (Safe Drinking Water Information System) data, which tracks contaminant testing results, compliance violations, and system characteristics for every public water system in the United States. A higher score indicates fewer detected contaminants, better compliance with federal regulations, and stronger infrastructure. However, no water system is perfect, and conditions can change due to aging pipes, seasonal variations, upstream pollution events, or changes in treatment processes. Regardless of your city's score, monitoring your local utility's annual Consumer Confidence Report and considering point-of-use filtration are prudent steps for protecting your household's water quality.
San Francisco has better overall water quality with a score of 86/100 (Grade A-). Higher overall quality score (86 vs 73)
Yes, San Francisco's tap water generally meets EPA safety standards with a quality score of 86/100 (Grade A-).
Los Angeles's tap water has some concerns with a score of 73/100. Consider using a water filter for additional protection.
Water filters can provide additional protection and improve taste regardless of your city's water quality score. Given the scores in this comparison, we particularly recommend filtration for residents of Los Angeles.