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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.
Water quality data for 12 cities serving 680,856 residents
Honolulu County in Hawaii has an average water quality score of 80/100 (Grade B+) based on analysis of 12 municipal water systems. The county's water systems serve approximately 680,856 residents.
Overall, Honolulu County demonstrates good water quality standards. 8 of 12 cities exceed the county average, with Waimalu leading with a score of 92/100.
12 cities ranked by water quality score
| Rank | City | Score | Grade | Population |
|---|---|---|---|---|
| 1 | Waimalu Top concern: Haloacetic Acids (17.4% of limit) | 92 | A | 13,373 |
| 2 | East Honolulu Top concern: Total Trihalomethanes (20.5% of limit) | 87 | A- | 48,538 |
| 3 | Mililani Town Top concern: Haloacetic Acids (20.2% of limit) | 87 | A- | 28,902 |
| 4 | Wahiawa Top concern: Copper (17.1% of limit) | 86 | A- | 19,628 |
| 5 | Ewa Gentry Top concern: Haloacetic Acids (21.7% of limit) | 85 | A- | 25,863 |
| 6 | Waipahu Top concern: Fluoride (15.6% of limit) | 83 | B+ | 43,673 |
| 7 | Mililani Mauka Top concern: Fluoride (17.6% of limit) | 83 | B+ | 25,461 |
| 8 | Kailua Top concern: Fluoride (18% of limit) | 82 | B+ | 42,702 |
| 9 | Pearl City Top concern: Total Trihalomethanes (37.4% of limit) | 72 | B- | 43,424 |
| 10 | Honolulu Top concern: Total Trihalomethanes (53.2% of limit) | 70 | B- | 343,284 |
| 11 | Makakilo Top concern: Lead (61.3% of limit) | 70 | B- | 13,466 |
| 12 | Kaneohe Top concern: Total Trihalomethanes (59.4% of limit) | 67 | C+ | 32,542 |
Top detected contaminants across county water systems
| Contaminant | Avg Level | Max Level | EPA Limit | % of Limit | Cities |
|---|---|---|---|---|---|
| Lead | 0.004 mg/L | 0.009 mg/L | 0.015 mg/L | 23.5% | 10 |
| Total Trihalomethanes | 16.77 ug/L | 47.527 ug/L | 80 ug/L | 21% | 12 |
| Fluoride | 0.823 mg/L | 1.348 mg/L | 4 mg/L | 20.6% | 11 |
| Haloacetic Acids | 11.877 ug/L | 30.283 ug/L | 60 ug/L | 19.8% | 10 |
| Nitrite | 0.181 mg/L | 0.471 mg/L | 1 mg/L | 18.1% | 11 |
| Arsenic | 0.002 mg/L | 0.005 mg/L | 0.01 mg/L | 17.8% | 12 |
| Copper | 0.213 mg/L | 0.757 mg/L | 1.3 mg/L | 16.4% | 11 |
| Nitrate | 1.492 mg/L | 4.25 mg/L | 10 mg/L | 14.9% | 12 |
Recent violations across county water systems
Showing 10 of 18 recent violations
Water quality in Honolulu County, Hawaii reflects the region's unique combination of water sources, treatment infrastructure, and environmental factors. Our comprehensive analysis examines 12 municipal water systems serving a combined population of over 680,856 residents.
The county shows strong water quality performance, with scores ranging from 67/100 in Kaneohe to 92/100 in Waimalu. This 25-point spread indicates significant variation in water quality across the county, suggesting different water sources or treatment approaches.
The most prevalent contaminants detected across Honolulu County water systems include Lead, Total Trihalomethanes, Fluoride. All monitored contaminants remain within acceptable levels relative to EPA Maximum Contaminant Levels (MCLs).
Honolulu County's water quality is generally good. Residents can feel confident in their tap water quality, though those with specific health concerns or sensitivity to certain contaminants may still benefit from filtration. Regular review of your city's annual Consumer Confidence Report is recommended.
Honolulu County has an average water quality score of 80/100 (Grade B+) based on analysis of 12 municipal water systems serving 680,856 residents.
Waimalu has the highest water quality score in Honolulu County at 92/100. View the detailed report for Waimalu.
Most cities in Honolulu County have water that meets EPA standards. However, a water filter can provide additional protection and improve taste. The need depends on your specific city and any personal health considerations.
Click on any city in the rankings table above to view its detailed water quality report, including contaminant levels, EPA compliance history, and filter recommendations.