Ohio tap water hardness in 40 cities, and 12 with no figure

What this dataset is

We took Ohio's 40 largest cities by Census Bureau 2024 population estimates^[21]. For each, we found the utility that serves it and read that utility's most recent water quality report or water quality web page for a total hardness figure. No figure here comes from a softener company, a hardness map or an estimate. The full table, with a source link for every row, is free to download as a CSV file.

Hardness is the amount of dissolved calcium and magnesium in water, usually stated as milligrams per liter (mg/L) of calcium carbonate. Softener and water heater makers often use grains per gallon (gpg) instead: 1 gpg is about 17.1 mg/L. The U.S. Geological Survey classifies water this way^[17]:

mg/L as calcium carbonate	USGS class
0 to 60	Soft
61 to 120	Moderately hard
121 to 180	Hard
More than 180	Very hard

What we found

1. In 12 of the 40 cities, the utility publishes no hardness figure. We read their current reports and water pages and found no number. That is legal: hardness has no federal health or secondary standard^[20], and the federal report rule does not require it^[19]. But it means residents in Toledo, Youngstown, Mansfield and nine other cities have to call to find out.
2. Canton is in a class of its own. Its three plants average 354, 429 and 497 mg/L (21, 25 and 29 gpg)^[1], about 3 to 4 times Columbus's 115^[10] or Cleveland's 117^[13]. Canton publishes these by plant on its website, not as a single system figure.
3. The other 23 ranked cities sit in a narrow band, from 98 mg/L (Dublin) to 147 mg/L (Springfield). Many Ohio utilities soften their water at the plant. Springfield's well water starts at 346.6 mg/L and leaves treatment at 147^[3]. Dayton's Mad River well field water starts at 320.06 mg/L and leaves the Ottawa plant at 149.59^[4].

Ohio water hardness by city, ranked

The ranking value is the utility's published average for its system, or for the plant that serves the city where we could confirm it. Canton publishes no system figure, so it is shown as its plant range and ranked on its lowest plant. Ties share a rank. Differences of a few mg/L are within normal variation between plants and seasons.

Rank	City	Hardness (mg/L)	gpg	USGS class	What the utility publishes	Source
1	Canton	354 to 497	21 to 29	Very hard	Plants: Northeast 429, Northwest 497, Sugarcreek 354 (undated web page)	[1]
2	Springfield	147	8.6	Hard	Average 147 after treatment, 2025	[3]
3	Dayton	139	8.1	Hard	Distribution system 138.53, 2025	[4]
3	Kettering	139	8.1	Hard	Buys from Dayton; Dayton distribution 138.53, 2025	[4][2]
5	Fairfield	132	7.7	Hard	2025 daily average 132	[7]
6	Hamilton	130	7.6	Hard	130, 2025	[8]
7	Westerville	128	7.5	Hard	Averages 128 (undated web page)	[9]
8	Cincinnati	126	7.4	Hard	Miller plant 126 (supplies about 88% of GCWW water); Bolton plant 140 (undated web page)	[6]
9	Grove City	125	7.3	Hard	Dublin Road plant 125, 2025	[10]
10	Delaware	121	7.1	Hard	121 (range 103 to 142), 2025	[11]
11	Newark	119	7.0	Moderately hard	119, 2025	[12]
12	Cleveland	117	6.8	Moderately hard	Average 117 (105 to 130), 2025	[13]
12	Cleveland Heights	117	6.8	Moderately hard	Cleveland Water	[13]
12	Euclid	117	6.8	Moderately hard	Cleveland Water	[13]
12	Lakewood	117	6.8	Moderately hard	Cleveland Water	[13]
12	Parma	117	6.8	Moderately hard	Cleveland Water	[13]
12	Strongsville	117	6.8	Moderately hard	Cleveland Water	[13]
18	Columbus	115	6.7	Moderately hard	System average 115, 2025; plants: Dublin Road 125, Hap Cremean 98, Parsons Avenue 123	[10]
18	Gahanna	115	6.7	Moderately hard	Columbus water	[10]
18	Hilliard	115	6.7	Moderately hard	Columbus water	[10]
18	Reynoldsburg	115	6.7	Moderately hard	Columbus water	[10]
18	Upper Arlington	115	6.7	Moderately hard	Columbus water	[10]
23	Akron	107	6.3	Moderately hard	107 (76 to 150), 2025	[15]
24	Dublin	98	5.7	Moderately hard	Hap Cremean plant 98 (85 to 118), 2025	[10]

Notes on specific rows:

• Kettering: its supplier, Montgomery County Environmental Services, buys its water from Dayton, so we rank it on Dayton's 2025 measured figure. MCES's own undated page says "approximately 9 grains per gallon (157 mg/L)"^[2].
• Dayton: the city's water quality web page still shows a 2010 average of 155 mg/L. We used the 2025 measured figure^[4].
• Grove City and Dublin: we read the serving plant from Columbus's service area map^[10]. Homes near plant boundaries may get blended water, closer to the 115 system average.

Published, but not comparable

City	What the utility publishes	Why it is not ranked	Source
Beavercreek	"8" with no unit, in a softener settings FAQ (undated)	A setting, not a measured average. Read as grains per gallon, it is about 137 mg/L	[5]
Mason	Greater Cincinnati Water Works plants: 126 and 140 mg/L	We could not confirm which plant serves Mason	[6]
Cuyahoga Falls	Treatment target: finished hardness 100 to 130 mg/L, 2025	No measured average published	[14]

Cities whose utility publishes no hardness figure

Toledo, Youngstown, Lorain, Middletown, Mansfield, Mentor, Huber Heights, Lancaster, Findlay, Warren, North Ridgeville and Marion. We read each utility's current report and water pages in October 2026. Figures for these cities on other websites come from third parties, not the utility. If you live in one of them, call the utility and ask for "total hardness as calcium carbonate."

We left Elyria out entirely. Its newest published figure is from its 2015 report, and the range printed beside it does not contain its own average.

What hardness means for your water heater

When hard water is heated, some of the minerals drop out as scale. In a tank heater, most of it settles on the bottom as sediment. In a tankless heater, it coats the narrow passages of the heat exchanger. A 2012 guide prepared for the U.S. Department of Energy's Building America program notes that scale can restrict flow through a tankless heat exchanger and shorten the unit's life^[18]. The same guide says that above about 8 to 14 grains per gallon (136 to 239 mg/L), manufacturers may require a water softener^[18].

Rinnai's SENSEI manual gives one maker's guidance^[16]:

Rinnai's label	mg/L	Grains per gallon	Rinnai's guidance
Soft	0 to 60	0 to 4	None
Slightly hard	61 to 120	4 to 7	Water softener or scale cutter recommended; flush residential units once a year
Moderately hard	121 to 160	7 to 9	Water softener or scale cutter recommended; flush residential units once a year
Very hard	161 to 200	9 to 12	Strongly recommended
Extremely hard	Over 200	12+	"Water Softener or Rinnai Scale Cutter is Required"

Rinnai's "very hard" is its own label and is not the same as the USGS class above. The manual also lists 200 mg/L as the maximum total hardness for these units and says replacement of components due to water quality damage is not covered by the warranty^[16]. All three Canton plants are above 200 mg/L^[1]. Every other ranked city falls in Rinnai's slightly or moderately hard bands. Other makers set their own limits, so read the manual for your unit before you buy or install one.

Method and limits

• Cities: the 40 largest incorporated places in Ohio by 2024 Census estimates^[21].
• Sources: the serving utility's 2025 report where it lists hardness, otherwise the utility's own water quality page. Undated pages are marked.
• Which utility: many suburbs buy water from a larger city. We matched each city to its supplier using the utility's service area map or the city's own report.
• Printed figures only: some reports also list calcium and magnesium separately, and those do not always add up to the printed hardness line. We report the hardness line as printed.
• One number per city is a simplification. Hardness varies by plant, by season and by address. Your utility's report, or a test at your tap, is the better figure for your home.
• Corrections: if a utility publishes a newer figure, see our corrections page and we will update the table.

When to call a pro

• Your area is over 200 mg/L and you are buying a tankless heater: ask an independent licensed plumber about scale control and the maker's warranty limits before install.
• A tank heater pops or rumbles, which usually means heavy sediment.
• A tankless unit shows a scale or service code.
• Your fixtures get white crust, or your heater's flush schedule keeps coming due.