Cincinnati, OH water hardness

Name: Cincinnati, OH water hardness as published by Greater Cincinnati Water Works
Creator: Greater Cincinnati Water Works
License: https://www.usa.gov/government-works

Greater Cincinnati Water Works does not publish one hardness figure for Cincinnati. It publishes 2 separate figures, one per plant, in its 2025 GCWW Water Quality Report. Across them the published numbers run from 126 to 140 mg/L. On the USGS scale those figures are all hard water, so the classification does not depend on which plant serves an address. Every published figure is in the table below.

Greater Cincinnati Water Works published a figure for each of 2 plants rather than one for the system; the bar spans the lowest and highest of those published figures, 126 to 140 mg/L. The plotted point is the midpoint of the lowest and highest figures published across this system's 2 areas; the utility publishes no system-wide figure, so this midpoint is not one of its numbers. Classification bands from the USGS Water Science School.

Every figure Greater Cincinnati Water Works publishes, by plant

These are the only hardness numbers this utility publishes. There is no system-wide figure to quote, so the figure plotted above is a midpoint we calculated from the lowest and highest of them, and it is labelled as such everywhere it appears.

Plant as published	mg/L (ppm)	Grains per gallon	USGS class
Richard Miller Plant	126	7	Hard
Charles M. Bolton Plant	140	8	Hard

Figures in the grains column are the utility's own where it published them. Where it published only one unit, the other column is our conversion at 17.1 mg/L per grain, and the row above says which. Nothing in this table is averaged across plants.

The published figures, exactly as they appear

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

Water from GCWW's Richard Miller Plant has an average hardness of 126 mg per liter or 7 grains per gallon. […] Water from the Charles M. Bolton Plant averages 140 mg per liter or 8 grains per gallon.
Greater Cincinnati Water Works, 2025 GCWW Water Quality Report

Units as published: mg per liter, with grains per gallon given alongside. What kind of figure it is: a single value. Retrieved 2026-10-17.

Cincinnati 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 span across areas	126	7	both published by the utility
High end of published span across areas	140	8	both published by the utility
Plotted on the scale above	133	7.8	midpoint of the lowest and highest figures published across this system's 2 areas; the utility publishes no system-wide figure, so this midpoint is not one of its numbers; 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: 133 ÷ 17.1 = 7.8 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	Greater Cincinnati Water Works
Service area as published	Greater Cincinnati Water Works' system, supplied by two treatment plants. The report does not say which addresses each plant serves.

Provenance of every number on this page

Source document	2025 GCWW Water Quality Report
Source URL	https://www.cincinnati-oh.gov/water/water-quality-and-treatment/water-quality-reports/latest/
Published by	Greater Cincinnati Water Works
Report year	2025
Year note	The hardness figures sit in the report's frequently-asked-questions section, not in its water-quality tables, and are given as plant averages with no sampling range.
Retrieved	2026-10-17
Classification bands	USGS Water Science School, retrieved 2026-10-16

Notes the report forces on this page

GCWW publishes a figure per treatment plant and no single system-wide figure. The plotted point is the midpoint of the two published plant averages and is not itself a GCWW number.
Both plant averages fall in the USGS hard band, so the classification on this page does not depend on which plant serves an address.
An undated GCWW frequently-asked-questions page at cincinnati-oh.gov gives different figures for the same two plants — 137 mg/L (8 grains per gallon) for Miller and 147 mg/L (9 grains per gallon) for Bolton. This page uses the dated 2025 report instead, and the undated page's figures are not published here.

If you are sizing a softener for Cincinnati water

At 7.8 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 Cincinnati 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.

Cincinnati, OH 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

Milwaukee, WI Milwaukee Water Works, 137 mg/L (8 gpg)
St. Louis, MO City of St. Louis Water Division, 138 mg/L (8.1 gpg)
Ann Arbor, MI City of Ann Arbor Water Treatment Services, 126 mg/L (7.4 gpg)
Philadelphia, PA Philadelphia Water Department, 125 mg/L (7.3 gpg)

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