Hardness depends on who supplies your water, not on the city name in your address. Around the Denver metro it runs from soft in Boulder to very hard in Thornton.
Water hardness by provider
| Where | Hardness | Rating | Source |
|---|---|---|---|
| Boulder City of Boulder | About 42 mg/L (2.4 gpg) | Soft | City of Boulder |
| Arvada City of Arvada | 2025 plant averages of 43 and 65 mg/L | Soft to moderately hard | Arvada 2026 report |
| Broomfield City and County of Broomfield | 25 to 130 mg/L in 2025 (1.5 to 7.3 gpg), depending on the blend | Soft to moderately hard | Broomfield 2025 report |
| Golden City of Golden | 40 to 170 mg/L, rising and falling with Clear Creek | Varies | City of Golden |
| Denver, Littleton, Greenwood Village, parts of Centennial, Lakewood, Wheat Ridge, and Lone Tree Denver Water | Average about 105 mg/L in 2025 (6.1 gpg), range 55 to 124 | Moderately hard | Denver Water 2026 report |
| Parker, Lone Tree east of I-25 Parker Water & Sanitation | Average 108 mg/L in 2025 (6.3 gpg), range 34 to 206 | Moderately hard, with wide swings | Parker Water 2026 report |
| Commerce City South Adams County Water & Sanitation | Softened to about 115 mg/L (7 gpg) at the Ennis plant | Moderately hard (after softening) | SACWSD Ennis plant |
| Northglenn City of Northglenn | About 120 mg/L (7 gpg), from 2019 sampling, the latest it publishes | Moderately hard | Northglenn 2026 report |
| Westminster City of Westminster | 112 to 152 mg/L in 2025 (about 7 to 9 gpg) | Moderately hard to hard | Westminster 2026 report |
| Aurora Aurora Water | Average 136 mg/L in 2025 (about 8 gpg), range 87 to 198 | Hard | Aurora Water 2026 report |
| Highlands Ranch Highlands Ranch Water | Typically 11 to 13 gpg (188 to 222 mg/L); 2025 quarterly averages ranged 74 to 263 | Hard to very hard | Highlands Ranch Water |
| Thornton City of Thornton | Average about 230 mg/L in 2025 (13.5 gpg), range 152 to 356 | Very hard | Thornton 2026 report |
From each provider's latest published water quality report or water page, checked October 2026. Englewood, Brighton, Louisville, Lafayette, Superior, Erie, East Cherry Creek Valley, and Consolidated Mutual didn't publish a hardness figure in their latest reports. Ratings use the common scale below.
What the numbers mean
Hardness is mostly dissolved calcium and magnesium. It's reported either in milligrams per liter (mg/L, the same as parts per million) or in grains per gallon (gpg). One grain per gallon is about 17.1 mg/L.
- Soft: 0 to 60 mg/L (up to about 3.5 gpg)
- Moderately hard: 61 to 120 mg/L (about 3.5 to 7 gpg)
- Hard: 121 to 180 mg/L (about 7 to 10.5 gpg)
- Very hard: over 180 mg/L (over about 10.5 gpg)
Why some cities swing so much
Many providers blend sources. Snowmelt is soft; groundwater and late-season river water are harder. Denver Water says its water is a little harder in winter and softer from late spring through fall, when runoff dilutes it. Golden's hardness follows the level of Clear Creek. Broomfield mixes its own treated water with Denver Water's. Highlands Ranch Water's 2025 quarterly averages ranged from 74 to 263 mg/L. If your fixtures scale up faster at certain times of year, that's why.
What hard water does to a house
- Water heaters collect sediment on the bottom of the tank, run longer, pop and rumble, and wear out sooner. Why water heaters pop →
- Tankless heaters scale up inside the heat exchanger and need regular descaling.
- Faucet cartridges, shower valves, and toilet fill valves stiffen and start dripping.
- Glass and fixtures spot, and soap doesn't lather well.
Do you need a softener?
Our rule of thumb: below about 3.5 gpg (60 mg/L), like Boulder's water, you don't. Above about 7 to 10 gpg, as in Thornton, Highlands Ranch, and at times in Aurora and Westminster, a properly sized softener usually earns its keep in a house you plan to stay in, mostly by protecting the water heater and fixtures. In between, it comes down to how much the scale bothers you. We can test the water at your tap and size a softener to your household. Water softeners →
Check your own water
Your provider's annual water quality report lists its hardness, and your water bill tells you which provider that is. Some districts, especially in Centennial, Lakewood, and Wheat Ridge, buy water from Denver Water; others treat their own.