How hard is the water in Centennial, CO?

Tap water hardness
96mg/L
5.6gpg
Moderately hard

Reported by Denver Water Board · October 2025

CO typical
97 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

Tap water in Centennial has about 96 mg/L of hardness, which is 5.6 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Denver Water Board, dated October 2025.

Centennial on the hardness scale, with nearby cities
060120180240300360+CO typical 97Cherry Creek: 96 mg/LCherry Creek 96Dove Valley: 96 mg/LDove Valley 96Greenwood Village: 96 mg/LGreenwood Village 96Meridian: 96 mg/LMeridian 96Cherry Hills Village: 96 mg/LCherry Hills Village 96Four Square Mile: 96 mg/LFour Square Mile 96Littleton: 97 mg/LLittleton 97Aurora: 100 mg/LAurora 100Englewood: 101 mg/LEnglewood 101Sheridan: 101 mg/LSheridan 101Centennial 96mg/L as calcium carbonate060120180240300360+CO 97Cherry Creek: 96 mg/LCherry Cre. 96Dove Valley: 96 mg/LDove Valley 96Greenwood Village: 96 mg/LGreenwood. 96Meridian: 96 mg/LMeridian 96Cherry Hills Village: 96 mg/LCherry Hil. 96Four Square Mile: 96 mg/LFour Squar. 9696 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 96 mg/L, Centennial is close to the typical Colorado figure of 97 mg/L. None of the 10 nearest cities we track has softer water. The range nearby runs from 96 mg/L in Cherry Creek to 101 in Englewood.

What 96 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.

Softener size for Centennial

3 people × 75 gallons a day × 5.6 gpg = 1,260 grains a day. A 24,000-grain unit regenerates about every 19 days.

Size it for your household

EPA record for Centennial's water system

Denver Water Board · PWSID CO0116001

No health-based violations since 2016

Serves about 1,287,000 people from surface water.

Health-based
0
Monitoring or reporting
35
Open now
0

TapWaterData ties Centennial to this system. EPA's service-area records do not name Centennial, so check the utility printed on your water bill.

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 Centennial water hard?

Somewhat. It measures about 96 mg/L (5.6 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Centennial in grains per gallon?

About 5.6 gpg. One grain per gallon equals 17.1 mg/L, so 96 mg/L divided by 17.1 gives 5.6.

What size water softener do I need in Centennial?

For 3 people using 75 gallons each per day, 5.6 gpg works out to about 1,260 grains a day. A 24,000-grain softener covers that with a regeneration about every 19 days.

Has the Centennial water system had EPA violations?

EPA records show no health-based violations for Denver Water Board since 2016. There were also 35 monitoring or reporting violations, which are about late or missing tests and notices.

Nearby cities

All 64 cities in Colorado

Hardness data: TapWaterData US Water Hardness (utility report, October 7, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.