Washington, DC water hardness

Name: Washington, DC water hardness as published by DC Water
Creator: DC Water
License: https://www.usa.gov/government-works

DC Water publishes a hardness range of 70 to 120 mg/L for its system, on the page cited below. On the USGS scale that is moderately hard water.

DC Water published a range of 70 to 120 mg/L, shown as the bar. The plotted point is the midpoint of the published range (no average is published). Classification bands from the USGS Water Science School.

The published figure, exactly as it appears

This is the hardness line transcribed from the source, with nothing added:

The hardness of the city's tap water is typically around 70 to 120 parts per million or 3 to 9 grains per gallon.
DC Water

Units as published: parts per million, with grains per gallon given alongside. What kind of figure it is: a range with no average. Retrieved 2026-10-17.

Washington hardness in mg/L and grains per gallon

Water-quality reports use mg/L (identical to ppm). Softener instructions and plumbing specifications use grains per gallon. Both are below. Where a figure is our arithmetic rather than the utility's own number, it says so.

Figure	mg/L (ppm)	Grains per gallon	Whose number
Low end of published range	70	3	both published by the utility
High end of published range	120	9	both published by the utility
Plotted on the scale above	95	5.6	midpoint of the published range (no average is published); the gpg here is our conversion at 17.1, so it can differ slightly from a utility’s own rounded gpg figure

The conversion, both ways: gpg = mg/L ÷ 17.1 and mg/L = gpg × 17.1. Worked for this system: 95 ÷ 17.1 = 5.6 gpg. The converter does °dH and °f as well, and why the factor is 17.1 explains where the number comes from.

What this figure does not tell you

Service area and source water

Utility	DC Water
Service area as published	The District of Columbia. The page refers only to “the city's tap water” and names no treatment plant or sub-area.

Provenance of every number on this page

Source document	DC Water, “How hard is the water in the District of Columbia?”
Source URL	https://www.dcwater.com/content/how-hard-water-district-columbia
Published by	DC Water
Report year	Not stated on the source page
Year note	The page states no year for the hardness figures and cites no report.
Retrieved	2026-10-17
Classification bands	USGS Water Science School, retrieved 2026-10-16

Notes the report forces on this page

DC Water's two published units do not convert into each other. At 17.1 mg/L per grain, 70 to 120 ppm is 4.1 to 7.0 grains per gallon, but the page publishes 3 to 9 grains per gallon — a wider span. Both of its figures are shown here as published and neither has been adjusted to fit the other.
The page gives no year and cites no report, so this figure cannot be tied to a sampling period.
The page states that hardness varies across the city and by season, peaking in warmer months and falling in winter, without giving numbers for that variation.

If you are sizing a softener for Washington water

At 5.6 gpg, the sizing arithmetic starts from your household's water use, not from the hardness alone. The calculator below is pre-filled with this system's figure and every other input is an editable assumption.

Whether a softener is worth installing at this hardness is a judgement, not arithmetic, and it is not one this site makes for you. Nothing here has been tested by the author.

Where Washington sits against other verified systems

Soft Soft 0–60

Moderately hard Moderate 61–120

Hard Hard 121–180

Very hard Very hard 181+

Portland, OR 9 mg/L 0.5 gpg Soft
Boston, MA 16 mg/L 1 gpg Soft
Manchester, NH 17.9 mg/L 1 gpg Soft
Raleigh, NC 25 mg/L 1.47 gpg Soft
New York, NY 32 mg/L 2 gpg Soft
Charlotte, NC 32 mg/L 1.9 gpg Soft
Memphis, TN 46 mg/L 2.7 gpg Soft
Anchorage, AK 56 mg/L 3.3 gpg Soft
Oakland, CA 68.4 mg/L 4 gpg Moderately hard
Nashville, TN 77.3 mg/L 4.5 gpg Moderately hard
Sacramento, CA 83 mg/L 4.9 gpg Moderately hard
Fresno, CA 89.3 mg/L 5.2 gpg Moderately hard
Saint Paul, MN 90 mg/L 5 gpg Moderately hard
Austin, TX 93 mg/L 5.4 gpg Moderately hard
Washington, DC 95 mg/L 5.6 gpg Moderately hard
Birmingham, AL 98 mg/L 5.7 gpg Moderately hard
Kansas City, MO 100 mg/L 5.8 gpg Moderately hard
Denver, CO 105 mg/L 6.1 gpg Moderately hard
Tulsa, OK 114.5 mg/L 6.7 gpg Moderately hard
Louisville, KY 115 mg/L 6.7 gpg Moderately hard
Columbus, OH 120 mg/L 7 gpg Moderately hard
Cleveland, OH 120 mg/L 7 gpg Moderately hard
Philadelphia, PA 125 mg/L 7.3 gpg Hard
Ann Arbor, MI 126 mg/L 7.4 gpg Hard
Cincinnati, OH 133 mg/L 7.8 gpg Hard
Milwaukee, WI 137 mg/L 8.01 gpg Hard
St. Louis, MO 138 mg/L 8.1 gpg Hard
Fort Worth, TX 145 mg/L 8.5 gpg Hard
Honolulu, HI 162.5 mg/L 9.5 gpg Hard
Wichita, KS 170 mg/L 9.9 gpg Hard
Omaha, NE 170 mg/L 10 gpg Hard
Los Angeles, CA 192 mg/L 11.2 gpg Very hard
Lincoln, NE 192 mg/L 11.2 gpg Very hard
Tampa, FL 220 mg/L 12.9 gpg Very hard
Phoenix, AZ 237 mg/L 13.9 gpg Very hard
Mesa, AZ 239.4 mg/L 14 gpg Very hard
San Diego, CA 276 mg/L 16 gpg Very hard
Las Vegas, NV 280 mg/L 16 gpg Very hard
Chandler, AZ 282.2 mg/L 16.5 gpg Very hard
San Antonio, TX 299.3 mg/L 17.5 gpg Very hard
Anaheim, CA 300 mg/L 18 gpg Very hard
Indianapolis, IN 317 mg/L 19 gpg Very hard
Madison, WI 324.9 mg/L 19 gpg Very hard
Scottsdale, AZ 352.5 mg/L 20.6 gpg Very hard

mg/L as calcium carbonate. Each classification band is drawn the same width, so the axis is not linear in mg/L.

Washington, DC is the highlighted row. Every other system on this chart has its own page with its own published figure and report date. Grains per gallon are the utility's own figure where it published one, and our conversion at 17.1 mg/L per grain where it did not.

Systems with similar published hardness

Austin, TX Austin Water, 93 mg/L (5.4 gpg)
Birmingham, AL Birmingham Water Works, 98 mg/L (5.7 gpg)
Kansas City, MO KC Water, 100 mg/L (5.8 gpg)
Saint Paul, MN Saint Paul Regional Water Services, 90 mg/L (5.3 gpg)

All 44 verified systems How to find hardness in your own utility's report If you are on a well instead