waterbycounty
EPA SDWIS

New Castle County Water Quality

New Castle County, Delaware

Water Grade

A

Water Score

86.0

Violations

0

State Rank

#1

of 3 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

A

Based on EPA compliance history and violation data

Water Score

86/100

Higher = better quality

Health Violations

0

Health-based violations

Violation Rate

0.0%

Systems with violations

Water Advisory: New Castle County

Water Verdict

New Castle County receives an excellent water quality assessment with a grade of A and a score of 86.0 out of 100. The water supply meets or exceeds federal safety standards, and residents can generally drink tap water with confidence.

Violation Context

New Castle County has recorded zero health-based violations, indicating that the water system has met all federal safety standards during the reporting period. The violation rate is zero per 1,000 residents, which is the best possible outcome.

Consumer Guidance

Tap water in New Castle 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. 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

New Castle County has better water quality than the average county in Delaware. Its water score is 19.9 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

54.8%

172 of 314 assessed

Moderate concern

Top Impairment Causes

  • 1

    HABITAT ASSESSMENT

  • 2

    NUTRIENTS

  • 3

    ENTEROCOCCUS

Source: EPA ATTAINS · Reporting cycle 2022

Impairment is determined under the Clean Water Act §303(d): a water body is impaired when it fails to meet state-defined quality standards for designated uses (drinking, recreation, aquatic life). Assessment coverage varies by state — counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

136

Active in the past 5 years

Measurements Recorded

86K

85,708 total readings

Most Measured

  • Physical
  • Nutrient
  • Inorganics, Major, Metals

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

276cfs

May 14, 6:30 PM UTC

vs Long-Term Average

54%

Well below typical

Primary Streamgage

BRANDYWINE CREEK AT WILMINGTON, DE

USGS site
01481500
Drainage area
314 sq mi
Long-term mean
509 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 New Castle County, Delaware?
New Castle County, Delaware has a drinking-water quality grade of A with a score of 86.0/100, based on EPA SDWIS compliance data. The county has 0 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in New Castle County?
New Castle County has 0 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Zero violations is an excellent record indicating consistent compliance with federal drinking water standards.
How healthy are the watersheds in New Castle County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 54.8% of New Castle County's 314 assessed water bodies are classified as impaired (172 impaired). The top reported causes are HABITAT ASSESSMENT, NUTRIENTS, ENTEROCOCCUS. Impairment means the water body fails to meet state quality standards for at least one designated use — drinking water source, recreation, aquatic life, or fish consumption. Note: watershed impairment doesn't always translate to tap-water issues; treatment plants can remove most regulated contaminants.
How much water-quality monitoring happens in New Castle County?
EPA's Water Quality Portal records 85,708 measurements from 136 monitoring sites in New Castle County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Inorganics, Major, Metals. 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 New Castle County right now?
New Castle County's primary USGS streamgage on the BRANDYWINE CREEK is currently reading 276 cubic feet per second — 54% of the long-term mean of 508.64 cfs. This is well below typical — often a signal of drought stress on source water. For genuine real-time data, visit waterdata.usgs.gov.
How does New Castle County water compare to the Delaware average?
New Castle County's SDWIS water quality score of 86.0/100 is higher than the Delaware state average of 66.1. The average water quality grade across Delaware is C, based on data from 3 counties with available SDWIS data.
Is tap water safe to drink in New Castle County?
Based on EPA SDWIS data, New Castle County has a water quality grade of A (86.0/100). 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 New Castle County have clean drinking water?
New Castle County has 0 health-based drinking water violations according to EPA records. With a water quality score of 86.0/100 and grade A, the county's drinking water meets EPA standards with no recorded health violations. 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 New Castle County rank for water quality in Delaware?
New Castle County ranks #1 out of 3 counties in Delaware by SDWIS water quality score (1 = best). With a score of 86.0/100, it falls in the top 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

Kent County

Delaware

C

56.8

Water score

Sussex County

Delaware

C

55.6

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.

Watershed health and impaired-waterway data from the EPA ATTAINS Clean Water Act §303(d) assessments — state-reported, EPA-finalized.

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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