Delaware Water Quality
Drinking water data for all 3 counties.
Avg SDWIS Compliance Index
68.3
Most Common Five-Year SDWIS Compliance Band
A
Counties with Data
3
of 3 total
County water atlas
Delaware water signals by county
A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to compare index ranges, recorded violation rates, or impaired watersheds without leaving the page.
Counties
3
Avg SDWIS index
68.3
Watersheds
3
ATTAINS counties
Monitoring
3
3 fresh USGS snapshots
State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values appear only for fresh pipeline snapshots, not as a continuously updated stream. County pages include the observation time and year.
Multi-source coverage in Delaware
Beyond Drinking Water
EPA SDWIS
3/ 3
counties with drinking-water compliance data
24 health violations statewide (5yr)
EPA ATTAINS
94.6%
avg impaired across 3 counties
565 of 597 assessed bodies impaired
EPA WQP
480
monitoring sites across 3 counties
220,612 total readings (5yr window)
USGS NWIS
3
counties with a fresh pipeline snapshot
1 above2 below
State atlas notes
What stands out in Delaware
County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.
Compliance spread
New Castle County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Sussex County has the lowest at 56.9/100. That is a 29.3 point gap inside one state.
Zero health violations
1
3+ health violations
2
Watershed pressure
The atlas impairment layer points to counties where assessed water bodies are most likely to miss state quality standards. Assessment density varies, so compare the percentage with the number of assessed bodies on the county page.
Lowest flow reads
Highest fresh streamflow pipeline snapshots: New Castle County (187%, observation 2026), Sussex County (40%, observation 2026), Kent County (18%, observation 2026). These are source-data observations, not household tap-water conclusions.
All Delaware Counties
| County | SDWIS Compliance Index |
|---|---|
| New Castle County | 86.2 |
| Kent County | 61.9 |
| Sussex County | 56.9 |
Frequently Asked Questions
Which Delaware county has the highest SDWIS Compliance Index?
What does the Five-Year SDWIS Compliance Band mean?
What does EPA ATTAINS report across Delaware?
Which USGS streamflow records are shown across Delaware?
Where can Delaware residents find current official information?
What does Water Quality Portal monitoring volume show in Delaware?
Data Sources
Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. The WaterByCounty SDWIS Compliance Index reflects the recorded rate and is not an EPA score.
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.