waterbycounty
EPA SDWIS

Honolulu County Water Quality

Honolulu County, Hawaii

Water Grade

A

Water Score

71.9

Violations

1

State Rank

#3

of 4 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

A

Based on EPA compliance history and violation data

Water Score

71.9/100

Higher = better quality

Health Violations

1

Health-based violations

Violation Rate

0.1%

Systems with violations

Water Advisory: Honolulu County

Water Verdict

Honolulu County receives a good water quality assessment with a grade of A and a score of 71.9 out of 100. While the water supply is generally safe, occasional monitoring gaps or minor contaminant detections may occur.

Violation Context

Honolulu County has recorded 1 health-based violation, meaning the water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 0.1 violations per 1,000 residents, this rate is relatively low compared to many U.S. counties.

Consumer Guidance

Tap water in Honolulu County is generally safe to drink based on available data. Residents should still review their utility's annual Consumer Confidence Report for transparency on detected contaminants. With 1 recorded health violation, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

Honolulu County has poorer water quality than the average county in Hawaii. Its water score is 6.7 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Past 5 years

Water Quality Monitoring

Monitoring Sites

191

Active in the past 5 years

Measurements Recorded

184K

184,499 total readings

Most Measured

  • Physical
  • Microbiological
  • Nutrient

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

514cfs

May 14, 7:00 PM UTC

vs Long-Term Average

1337%

Well above typical

Primary Streamgage

Waikele Str at Waipahu, Oahu, HI

USGS site
16213000
Drainage area
45.14 sq mi
Long-term mean
38.5 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges — this view summarizes the primary one. The long-term mean is the full-record annual average; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in Honolulu County, Hawaii?
Honolulu County, Hawaii has a drinking-water quality grade of A with a score of 71.9/100, based on EPA SDWIS compliance data. The county has 1 health-based drinking water violation over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Honolulu County?
Honolulu County has 1 health-based drinking water violation recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How much water-quality monitoring happens in Honolulu County?
EPA's Water Quality Portal records 184,499 measurements from 191 monitoring sites in Honolulu County over the past five years. The most frequently measured characteristic groups are Physical, Microbiological, Nutrient. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in Honolulu County right now?
Honolulu County's primary USGS streamgage on the Waikele Str is currently reading 514 cubic feet per second — 1337% of the long-term mean of 38.45 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For genuine real-time data, visit waterdata.usgs.gov.
How does Honolulu County water compare to the Hawaii average?
Honolulu County's SDWIS water quality score of 71.9/100 is lower than the Hawaii state average of 78.6. The average water quality grade across Hawaii is B, based on data from 4 counties with available SDWIS data.
Is tap water safe to drink in Honolulu County?
Based on EPA SDWIS data, Honolulu County has a water quality grade of A (71.9/100). This indicates good to excellent water quality with strong SDWIS compliance. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Does Honolulu County have clean drinking water?
Honolulu County has 1 health-based drinking water violation according to EPA records. With a water quality score of 71.9/100 and grade A, the county's drinking water has had some compliance issues but continues to be monitored. Note: drinking-water compliance speaks to the public water system, not necessarily to the watershed itself — check the Watershed Health zone for ATTAINS §303(d) data.
How does Honolulu County rank for water quality in Hawaii?
Honolulu County ranks #3 out of 4 counties in Hawaii by SDWIS water quality score (1 = best). With a score of 71.9/100, it falls in the middle third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Hawaii County

Hawaii

A

70.6

Water score

Kauai County

Hawaii

A

86.0

Water score

Maui County

Hawaii

A

86.0

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP) — federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS) — continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

By Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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