Water Quality in Decatur, IL

Decatur's water has very hard water (191 PPM). A water softener is recommended to protect plumbing and appliances. Read below for a full breakdown.

City of Decatur · Source: Lake Decatur · Serves 69,047 residents

191
Hardness (PPM)
346
TDS (PPM)
0.9
Chlorine (mg/L)
4
PFAS (ppt)
3
Lead (ppb)
191 PPM 0 400 Very Hard
CONTAMINANT LEVELS Hardness 191 PPM TDS 346 PPM PFAS 4 ppt Lead 3 ppb Chlorine 0.9 mg/L Nitrate 4 mg/L

Hardness Scale: Where Decatur Falls

Soft 060120180250400+
Very hard water

Decatur's Lake Decatur supply is very hard. The Sangamon River watershed flows through limestone and glacial deposits.

What Decatur's Water Means for Your Home

Decatur residents deal with some of the hardest municipal water in the country. At 191 PPM (11.2 grains per gallon), the water contains high concentrations of dissolved calcium and magnesium picked up from the regional geology as surface water is treated and distributed. This is not a safety issue. The minerals are safe to consume. But they create real, measurable costs for homeowners. Hard water at 191 PPM costs the average household $800 to $1,200 per year in hidden expenses, including higher energy bills from scale-insulated water heaters, increased soap and detergent usage, and premature appliance failure. Many Decatur homeowners discover this only after a water heater replacement or plumber visit.

Beyond hardness, Decatur's water quality is generally within EPA guidelines for regulated contaminants. Chlorine is present at 0.9 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)191 PPM< 60 PPMNo federal limit⚠ Very Hard
Total Dissolved Solids346 PPM< 300 PPM500 PPM⚠ Elevated
PFAS (total)4 ppt4 ppt (EPA)4 ppt (2024)✓ OK
Lead3 ppb0 ppb (no safe level)15 ppb (action level)✓ Low
Chlorine / Chloramine0.9 mg/LTaste threshold ~1.04.0 mg/L✓ Normal
Nitrate4 mg/L5 mg/L10 mg/L✓ OK

Recommendations for Decatur Homes

🧂 Water Softener
At 191 PPM (11.2 GPG), Decatur's water is very hard. Scale will accumulate in pipes, water heaters, and on fixtures. A salt-based ion exchange softener removes the calcium and magnesium causing the problem. For a typical Decatur household of 2 to 4 people, a 48,000-grain softener is the right starting size.
Learn more about this solution →

About Decatur's Water Supply

Water Utility: City of Decatur

Water Source: Lake Decatur

Population Served: 69,047

Hardness: 191 PPM (11.2 grains per gallon)

Water quality can vary by neighborhood and season. The values above represent typical averages reported by City of Decatur. 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 Decatur to Other Illinois Cities

Chicago

140 PPM · Hard

Naperville

220 PPM · Very Hard

Rockford

185 PPM · Very Hard

Springfield

227 PPM · Very Hard

Peoria

231 PPM · Very Hard

Joliet

279 PPM · Extremely Hard

Frequently Asked Questions About Decatur Water

Is Decatur tap water safe to drink?
Decatur'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 Decatur?
Yes. At 191 PPM (11.2 GPG), Decatur's water is very hard. Without a softener, expect visible scale buildup on faucets and shower heads, reduced water heater efficiency (15 to 25 percent higher energy costs), spotted dishes and glassware, and soap that does not lather well. A salt-based water softener is the standard solution. For a typical Decatur home with 2 to 4 residents, a 48,000-grain system is the most common starting size.
What water filter is best for Decatur?
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 Decatur's water come from?
Decatur's drinking water is sourced from Lake Decatur and treated by City of Decatur. Decatur's Lake Decatur supply is very hard. The Sangamon River watershed flows through limestone and glacial deposits.
What is the hardness of Decatur water in grains per gallon?
Decatur's water hardness is 11.2 grains per gallon (GPG), which equals 191 parts per million (PPM). This is classified as very hard. Most water softener manufacturers recommend treatment above 7 GPG. To convert: 1 GPG = 17.1 PPM.
Does Decatur water damage tankless water heaters?
Yes. Most tankless water heater manufacturers recommend water hardness below 7 to 11 GPG (120 to 188 PPM). At 11.2 GPG, Decatur's water exceeds this threshold. Scale buildup inside the heat exchanger reduces efficiency and can void the manufacturer's warranty. A water softener installed upstream of the tankless heater is the standard solution.
Is Decatur water safe for babies and infants?
Decatur'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.
How much does hard water cost a Decatur household per year?
At 191 PPM, hard water costs the average Decatur household an estimated $800 to $1,200 per year in hidden costs. This includes 15 to 25 percent higher water heating bills from scale insulation, 50 to 75 percent more soap and detergent usage, shorter appliance lifespans (water heaters, dishwashers, washing machines), and increased plumbing maintenance. A water softener typically costs $600 to $1,500 installed and $50 to $100 per year in salt, which means most Decatur households see a return on investment within 1 to 2 years.

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