waterbycounty
Compiled federal source snapshot

Maryland Water Quality

Drinking water data for all 24 counties.

Avg SDWIS Compliance Index

45.8

Most Common Five-Year SDWIS Compliance Band

F

Counties with Data

24

of 24 total

County water atlas

Maryland 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

24

Avg SDWIS index

45.8

Watersheds

24

ATTAINS counties

Monitoring

24

22 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.

Prepared by ByCounty Editorial TeamPublished by WaterByCounty

Multi-source coverage in Maryland

Beyond Drinking Water

EPA SDWIS

24/ 24

counties with drinking-water compliance data

168 health violations statewide (5yr)

EPA ATTAINS

71.2%

avg impaired across 24 counties

786 of 1,109 assessed bodies impaired

EPA WQP

1,923

monitoring sites across 24 counties

1,110,680 total readings (5yr window)

USGS NWIS

22

counties with a fresh pipeline snapshot

2 above20 below

State atlas notes

What stands out in Maryland

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

Montgomery County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Baltimore County has the lowest at 15.7/100. That is a 70.5 point gap inside one state.

Zero health violations

1

3+ health violations

19

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.

Baltimore County86.1%Dorchester County83.0%Calvert County82.1%

Monitoring hubs

Anne Arundel County366 sitesSt. Mary's County187 sitesDorchester County158 sites

Lowest flow reads

Caroline County12%Wicomico County12%Carroll County13%

Highest fresh streamflow pipeline snapshots: Prince George's County (156%, observation 2026), Charles County (118%, observation 2026), Baltimore city (82%, observation 2026). These are source-data observations, not household tap-water conclusions.

All Maryland Counties

CountySDWIS Compliance Index
Montgomery County86.2
Baltimore city71.9
Howard County70.3
Anne Arundel County68.5
Frederick County65.4
Harford County61.3
Charles County58.1
Carroll County55.4
Washington County55.2
Prince George's County52.9
St. Mary's County52.7
Allegany County48.3
Calvert County44.7
Worcester County43.7
Kent County40.9
Dorchester County38.6
Wicomico County29.5
Talbot County29.0
Queen Anne's County27.2
Garrett County22.8
Somerset County22.0
Caroline County19.8
Cecil County18.2
Baltimore County15.7

Frequently Asked Questions

Which Maryland county has the highest SDWIS Compliance Index?
Montgomery County has the highest SDWIS Compliance Index in the published Maryland cohort at 86.2/100. This WaterByCounty relative comparison is not an EPA score and does not establish current conditions for a utility or address.
What does the Five-Year SDWIS Compliance Band mean?
The band is derived only from each county aggregation's recorded health-violation rate per 100,000 people served for the stated five-year source window. It is separate from the relative SDWIS Compliance Index and is not a current determination for a specific utility or address.
What does EPA ATTAINS report across Maryland?
Across 24 published Maryland county records with EPA ATTAINS data, 786 of 1,109 assessed water bodies are listed as impaired. This is a watershed assessment and does not describe finished household tap water.
Which USGS streamflow records are shown across Maryland?
WaterByCounty has 22 fresh USGS pipeline snapshots in the published Maryland cohort. Each county page shows its observation timestamp and year. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.
Where can Maryland residents find current official information?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. WaterByCounty's county-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.
What does Water Quality Portal monitoring volume show in Maryland?
The published county records contain 1,110,680 results from 1,923 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

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.

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