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Federal water data

County water report

Hawaii County Water Report

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

Water grade

A

Water score

70.6

State rank

#4

of 4

Health violations

1

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

207

36,713 recent measurements

Live streamflow

20%

Wailuku River at Piihonua, HI

Water at a glance

Key Water Indicators for Hawaii County

EPA SDWIS

Safety Grade

A

Score: 70.6 / 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

20% of mean

Wailuku River at Piihonua, HI

EPA WQP

Monitoring Sites

207

36,713 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.

70.6/100

Health violations

1

Health-based violations

Violations per 100K served

0.7

Population-normalized SDWIS rate

Editorial analysis

Understanding Hawaii County’s Water

Drinking Water Quality Overview

EPA SDWIS

Hawaii County earns an A grade for drinking water quality, scoring 70.6 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 2026-05-14T08:50:00.000-10:00) puts Wailuku River at 50.9 cfs — well below its long-term average at 20% of mean — low-flow conditions worth noting for water-dependent ecosystems. 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. Hawaii County has extensive coverage with 207 active monitoring sites with 36,713 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 Hawaii County

Water Verdict

Hawaii County, Hawaii receives a good water quality assessment with a grade of A and a score of 70.6 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 220 square miles of upstream watershed, giving local source waters a regional footprint. At the most recent USGS reading, local streamflow was below its historical mean at 19.8% — worth watching in drier seasons.

Violation Context

EPA SDWIS records for Hawaii County, Hawaii show 1 health-based violation, meaning a water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 0.7 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: 36,713 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 Hawaii County earns a Grade A overall with a small number of isolated health violations in the recent record. Hawaii County's drinking-water compliance score is 70.6 out of 100. The violation rate for Hawaii County is 0.7 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 207 active water-quality monitoring sites in Hawaii County, data coverage is strong. A pipeline streamflow snapshot from the Wailuku River gauge is also available on this page.

Regional Context

Hawaii County has poorer water quality than the average county in Hawaii. Its water score is 8 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 Hawaii County's water environment

Official EPA Resources for Hawaii County

EPA How's My Waterway

Interactive watershed health data for Hawaii County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Hawaii County

Consumer Confidence Reports (HI)

Annual water quality reports from utilities in Hawaii

Past 5 years

Water Quality Monitoring

Monitoring Sites

207

Active in the past 5 years

Measurements Recorded

37K

36,713 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

50.9cfs

May 14, 6:50 PM UTC

vs Long-Term Average

20%

Well below typical

Primary Streamgage

Wailuku River at Piihonua, HI

USGS site
16704000
Drainage area
220 sq mi
Long-term mean
257 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.

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Water Cost Estimate

3

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Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Hawaii 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 Hawaii County, Hawaii?
Hawaii County, Hawaii has a drinking-water quality grade of A with a score of 70.6/100, 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 Hawaii County?
Hawaii 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 Hawaii County?
EPA's Water Quality Portal records 36,713 measurements from 207 monitoring sites in Hawaii 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 Hawaii County right now?
Hawaii County's primary USGS streamgage on the Wailuku River has a pipeline snapshot of 50.9 cubic feet per second — 20% of the long-term mean of 256.99 cfs. This is well below typical — often a signal of drought stress on source water. For the latest gauge feed, visit waterdata.usgs.gov.
How does Hawaii County water compare to the Hawaii average?
Hawaii County's SDWIS water quality score of 70.6/100 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 Hawaii County?
Based on EPA SDWIS data, Hawaii County has a water quality grade of A (70.6/100). 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 Hawaii County have clean drinking water?
Hawaii County has 1 health-based drinking water violation according to EPA records. With a water quality score of 70.6/100 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 Hawaii County rank for water quality in Hawaii?
Hawaii County ranks #4 out of 4 counties in Hawaii by SDWIS water quality score (1 = best). With a score of 70.6/100, it falls in the bottom 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

Honolulu County

Hawaii

A

71.9

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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