Water Quality in Thornton, CO

Thornton's water quality is good overall. Hardness is low at 78 PPM, and no contaminants exceed health guidelines. Most homes here do not need a water softener.

City of Thornton · Source: Thornton reservoirs, Standley Lake · Serves 141,867 residents

78
Hardness (PPM)
113
TDS (PPM)
0.6
Chlorine (mg/L)
4
PFAS (ppt)
1
Lead (ppb)
78 PPM 0 400 Moderately Hard
CONTAMINANT LEVELS Hardness 78 PPM TDS 113 PPM PFAS 4 ppt Lead 1 ppb Chlorine 0.6 mg/L Nitrate 1 mg/L

Hardness Scale: Where Thornton Falls

Soft 060120180250400+
Generally good quality

Thornton's own reservoir system produces water with moderate hardness typical of the northern Front Range.

What Thornton's Water Means for Your Home

Thornton's water is moderately hard at 78 PPM. At this level, hard water is not a significant concern for most households. Scale buildup is minimal, and a water softener would provide little measurable benefit. If you are considering water treatment in Thornton, focus on contaminant filtration rather than softening.

Beyond hardness, Thornton's water quality is generally within EPA guidelines for regulated contaminants. Chlorine is present at 0.6 mg/L as a disinfectant residual, which is normal for municipal water systems. If you notice a pool-like taste or experience dry skin, a whole-house carbon filter is the most common and affordable solution. For homeowners who want to understand the full picture, requesting your utility's annual Consumer Confidence Report provides neighborhood-level data.

ContaminantDetectedHealth GuidelineLegal LimitStatus
Hardness (as CaCO₃)78 PPM< 60 PPMNo federal limit✓ OK
Total Dissolved Solids113 PPM< 300 PPM500 PPM✓ OK
PFAS (total)4 ppt4 ppt (EPA)4 ppt (2024)✓ OK
Lead1 ppb0 ppb (no safe level)15 ppb (action level)✓ Low
Chlorine / Chloramine0.6 mg/LTaste threshold ~1.04.0 mg/L✓ Normal
Nitrate1 mg/L5 mg/L10 mg/L✓ OK

Recommendations for Thornton Homes

🔄 Salt-Free Conditioner (Optional)
At 78 PPM, Thornton's water is moderately hard. Scale buildup is slow but noticeable over years, especially in tankless water heaters. A salt-free conditioner is a low-maintenance option if you want to extend appliance life.
Learn more about this solution →

About Thornton's Water Supply

Water Utility: City of Thornton

Water Source: Thornton reservoirs, Standley Lake

Population Served: 141,867

Hardness: 78 PPM (4.6 grains per gallon)

Water quality can vary by neighborhood and season. The values above represent typical averages reported by City of Thornton. To get exact numbers for your address, request a copy of the most recent Consumer Confidence Report (CCR) from your utility, or have your water independently tested.

Compare Thornton to Other Colorado Cities

Denver

90 PPM · Moderately Hard

Colorado Springs

101 PPM · Moderately Hard

Aurora

73 PPM · Moderately Hard

Lakewood

73 PPM · Moderately Hard

Arvada

81 PPM · Moderately Hard

Westminster

66 PPM · Moderately Hard

Frequently Asked Questions About Thornton Water

Is Thornton tap water safe to drink?
Thornton's water meets EPA legal standards for drinking water safety. However, legal limits and health-optimal levels are different things. Review the contaminant table above for specific numbers and how they compare to both legal limits and health guidelines.
Do I need a water softener in Thornton?
At 78 PPM, Thornton's water is moderately hard. Some homeowners at this level do not notice problems, while others see spotting on glassware, film on shower doors, or reduced soap lathering. Homes with tankless water heaters at this hardness level should strongly consider at least a salt-free conditioner, as scale buildup inside the heat exchanger can void the warranty. For other homes, it depends on your sensitivity and fixtures.
What water filter is best for Thornton?
The best filter depends on which contaminants you want to address. See our softener vs. filter guide to understand the difference between these categories.
Where does Thornton's water come from?
Thornton's drinking water is sourced from Thornton reservoirs, Standley Lake and treated by City of Thornton. Thornton's own reservoir system produces water with moderate hardness typical of the northern Front Range..
What is the hardness of Thornton water in grains per gallon?
Thornton's water hardness is 4.6 grains per gallon (GPG), which equals 78 parts per million (PPM). This is classified as moderately hard. To convert: 1 GPG = 17.1 PPM.
Does Thornton water damage tankless water heaters?
At 4.6 GPG, Thornton's water is unlikely to cause significant issues for tankless water heaters. However, if you notice reduced flow or efficiency over time, scale buildup could be a factor. Annual flushing with vinegar is good maintenance regardless of hardness.
Is Thornton water safe for babies and infants?
Thornton's water meets all EPA safety standards and is generally considered safe for preparing infant formula. The hardness minerals (calcium and magnesium) are not harmful. If your home has older plumbing, running cold water for 30 seconds before use is a good precaution to flush any lead from pipes.

Data sources. Water quality data compiled from EPA SDWIS, EWG Tap Water Database, USGS water hardness studies, and the City of Thornton Consumer Confidence Report. Hardness and contaminant levels represent typical average values and may vary by neighborhood and season. Last updated: 2026-02-12.