How hard is the water in Washington, DC?
Reported by D.C. Water and Sewer Authority · October 2025
- DC typical
- 117 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
Tap water in Washington has about 117 mg/L of hardness, which is 6.8 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from D.C. Water and Sewer Authority, dated October 2025.
What 117 mg/L means at home
You may see faint white spots on glasses and shower doors after the water dries.
Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.
Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.
What to do about it
Optional. Plenty of households at this level live with it and descale the kettle now and then.
Water softener
Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.
Carbon filter
Improves taste and removes chlorine. It leaves calcium and magnesium in place.
3 people × 75 gallons a day × 6.8 gpg = 1,539 grains a day. A 24,000-grain unit regenerates about every 15 days.
EPA record for Washington's water system
No health-based violations since 2016
Serves about 632,323 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 4
- Open now
- 0
Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.
Questions
Is Washington water hard?
Somewhat. It measures about 117 mg/L (6.8 grains per gallon), which the USGS classes as moderately hard.
What is the water hardness in Washington in grains per gallon?
About 6.8 gpg. One grain per gallon equals 17.1 mg/L, so 117 mg/L divided by 17.1 gives 6.8.
What size water softener do I need in Washington?
For 3 people using 75 gallons each per day, 6.8 gpg works out to about 1,539 grains a day. A 24,000-grain softener covers that with a regeneration about every 15 days.
Has the Washington water system had EPA violations?
EPA records show no health-based violations for D.C. Water and Sewer Authority since 2016. There were also 4 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
All 1 cities in District of Columbia
Hardness data: TapWaterData US Water Hardness (utility report, October 10, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.