How hard is the water in Thornton, CO?

Tap water hardness
98mg/L
5.8gpg
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 Thornton has about 98 mg/L of hardness, which is 5.8 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Denver Water Board, dated October 2025.

Thornton on the hardness scale, with nearby cities
060120180240300360+CO typical 97Broomfield: 46 mg/LBroomfield 46Derby: 79 mg/LDerby 79Commerce City: 95 mg/LCommerce City 95Welby: 96 mg/LWelby 96Twin Lakes: 99 mg/LTwin Lakes 99Sherrelwood: 100 mg/LSherrelwood 100Westminster: 100 mg/LWestminster 100Northglenn: 118 mg/LNorthglenn 118Federal Heights: 119 mg/LFederal Heights 119Shaw Heights: 127 mg/LShaw Heights 127Thornton 98mg/L as calcium carbonate060120180240300360+CO 97Broomfield: 46 mg/LBroomfield 46Derby: 79 mg/LDerby 79Welby: 96 mg/LWelby 96Sherrelwood: 100 mg/LSherrelwood 100Northglenn: 118 mg/LNorthglenn 118Federal Heights: 119 mg/LFederal He. 11998 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 98 mg/L, Thornton is close to the typical Colorado figure of 97 mg/L. Of the 10 nearest cities we track, 4 have softer water and 6 have harder. The range nearby runs from 46 mg/L in Broomfield to 127 in Shaw Heights.

What 98 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 Thornton

3 people × 75 gallons a day × 5.8 gpg = 1,296 grains a day. A 24,000-grain unit regenerates about every 18 days.

Size it for your household

EPA record for Thornton's water system

Thornton City of · PWSID CO0101150

No health-based violations since 2016

Serves about 226,465 people from surface water.

Health-based
0
Monitoring or reporting
8
Open now
0

EPA lists Thornton City of as the system serving Thornton. The hardness figure above comes from a different system's report, which TapWaterData uses for Thornton.

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 Thornton water hard?

Somewhat. It measures about 98 mg/L (5.8 grains per gallon), which the USGS classes as moderately hard.

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

About 5.8 gpg. One grain per gallon equals 17.1 mg/L, so 98 mg/L divided by 17.1 gives 5.8.

What size water softener do I need in Thornton?

For 3 people using 75 gallons each per day, 5.8 gpg works out to about 1,296 grains a day. A 24,000-grain softener covers that with a regeneration about every 18 days.

Has the Thornton water system had EPA violations?

EPA records show no health-based violations for Thornton City of since 2016. There were also 8 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.