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County water report

Honolulu County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Honolulu County, Hawaii.

Water grade

A

Water score

71.9

State rank

#3

of 4

Health violations

1

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

191

184,499 recent measurements

Live streamflow

1337%

Waikele Str at Waipahu, Oahu, HI

Water at a glance

Key Water Indicators for Honolulu County

EPA SDWIS

Safety Grade

A

Score: 71.9 / 100

EPA SDWIS

Active Violations

1

5-year health-based lookback

EPA ATTAINS

Watershed Health

Not reported

Coverage varies by state

USGS NWIS

Streamflow Snapshot

1337% of mean

Waikele Str at Waipahu, Oahu, HI

EPA WQP

Monitoring Sites

191

184,499 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

A

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

71.9/100

Health violations

1

Health-based violations

Violations per 100K served

0.1

Population-normalized SDWIS rate

Editorial analysis

Understanding Honolulu County’s Water

Drinking Water Quality Overview

EPA SDWIS

Honolulu County earns an A grade for drinking water quality, scoring 71.9 out of 100. Over the past five years, EPA SDWIS records 1 health-based violation — a single incident worth monitoring.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T09:00:00.000-10:00) puts Waikele Str at 514.0 cfs — running significantly above its long-term average at 1337% of mean flow. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Honolulu County has extensive coverage with 191 active monitoring sites with 184,499 recent measurements on record. Predominant monitoring categories include physical and microbiological. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.

Editorial advisory

What the data suggests for Honolulu County

Water Verdict

Honolulu County, Hawaii 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. The county's primary USGS gauge drains roughly 45 square miles of upstream watershed, giving local source waters a regional footprint. At the most recent USGS reading, local streamflow was running above its historical mean at 1336.7%.

Violation Context

EPA SDWIS records for Honolulu County, Hawaii show 1 health-based violation, meaning a water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 0.1 violations per 100,000 people served, this rate is relatively low compared to many U.S. counties. This compliance record sits alongside an unusually deep monitoring archive: 184,499 water-quality results have been logged across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Tap water in Honolulu County earns a Grade A overall with a small number of isolated health violations in the recent record. Honolulu County's drinking-water compliance score is 71.9 out of 100. The violation rate for Honolulu County is 0.1 per 100,000 people served. These violations were likely resolved quickly; Grade A reflects a strong multi-year compliance trend. Reviewing the most recent Consumer Confidence Report will show exactly which systems were affected and what corrective action was taken. With 191 active water-quality monitoring sites in Honolulu County, data coverage is strong. A pipeline streamflow snapshot from the Waikele Str gauge is also available on this page.

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.

Advisory text summarizes county-level public records and is not a replacement for your utility's current Consumer Confidence Report or direct local notices.

Contaminants & Resources

Key issues flagged in Honolulu County's water environment

Official EPA Resources for Honolulu County

EPA How's My Waterway

Interactive watershed health data for Honolulu County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Honolulu County

Consumer Confidence Reports (HI)

Annual water quality reports from utilities in Hawaii

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; the percent-of-typical value compares the latest reading against that average.

Free tool

Estimate Your Water Costs

Water Cost Estimate

3

3 people  ·  ~225 gal/day

Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Honolulu County:C — Moderate

Some violations or watershed impairment detected.

Estimates use the national average residential water rate ($0.0068/gal, EPA/AWWA 2023) and EPA WaterSense per-person consumption baseline (75 gal/person/day). Actual bills vary by utility, usage tier, and local infrastructure fees. For informational purposes only.

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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 streamflow snapshots 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 has a pipeline snapshot of 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 the latest gauge feed, 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 Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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