Boulder, CO water hardness

Tap water hardness
41mg/L
2.4gpg
Soft

Reported by Boulder City of · October 2025

CO typical
97 mg/L
EPA health violations since 2016
2
Data
Utility report

The water in Boulder carries roughly 41 mg/L of dissolved calcium and magnesium, or 2.4 grains per gallon. That is soft water. The number comes from Boulder City of, dated October 2025.

Boulder on the hardness scale, with nearby cities
060120180240300360+CO typical 97Longmont: 20 mg/LLongmont 20Louisville: 32 mg/LLouisville 32Erie: 33 mg/LErie 33Broomfield: 46 mg/LBroomfield 46Lafayette: 91 mg/LLafayette 91Arvada: 93 mg/LArvada 93Westminster: 100 mg/LWestminster 100Northglenn: 118 mg/LNorthglenn 118Federal Heights: 119 mg/LFederal Heights 119Shaw Heights: 127 mg/LShaw Heights 127Boulder 41mg/L as calcium carbonate060120180240300360+CO 97Longmont: 20 mg/LLongmont 20Louisville: 32 mg/LLouisville 32Erie: 33 mg/LErie 33Broomfield: 46 mg/LBroomfield 46Lafayette: 91 mg/LLafayette 91Westminster: 100 mg/LWestminster 10041 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 41 mg/L, Boulder is 56 mg/L below the typical Colorado figure of 97. Of the 10 nearest cities we track, 3 have softer water and 7 have harder. The range nearby runs from 20 mg/L in Longmont to 127 in Shaw Heights.

What 41 mg/L means at home

Soap and shampoo lather with very little product. Kettles and showerheads stay mostly free of white crust.

Some people notice that soap feels slow to rinse off in soft water. That slippery feel is normal and harmless.

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

Nothing, as far as hardness goes. At 41 mg/L a softener would have almost nothing to remove.

Carbon filter

If the water tastes of chlorine, a pitcher or faucet carbon filter takes care of that. It does not change hardness.

EPA record for Boulder's water system

Boulder City of · PWSID CO0107152

2 health-based violations since 2016

Serves about 166,080 people from surface water.

Health-based
2
Monitoring or reporting
5
Open now
0
20162017201820192020202120222023202420252026Haloacetic acids (HAA5)'16'18'20'22'24'26Haloacetic acids (HAA5)
Each dot is one health-based violation, placed at the start of its compliance period.
Contaminant or ruleViolationsPeriodStatus
Haloacetic acids (HAA5)a disinfection byproduct22017Resolved

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 Boulder water hard?

No. It measures about 41 mg/L (2.4 grains per gallon), which the USGS classes as soft.

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

About 2.4 gpg. One grain per gallon equals 17.1 mg/L, so 41 mg/L divided by 17.1 gives 2.4.

Has the Boulder water system had EPA violations?

EPA records show 2 health-based violations for Boulder City of since 2016, involving Haloacetic acids (HAA5). There were also 5 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 8, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.