Hard water in Northbrook, IL
Reported by Glenbrook SD · July 2025
- IL typical
- 139 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Northbrook carries roughly 131 mg/L of dissolved calcium and magnesium, or 7.7 grains per gallon. That is hard water. The number comes from Glenbrook SD, dated July 2025.
Northbrook sits close to the typical Illinois figure of 139 mg/L. Of the 10 nearest cities we track, 2 have softer water and 8 have harder. The range nearby runs from 112 mg/L in Mount Prospect to 380 in Lincolnshire.
What 131 mg/L means at home
Expect white crust on faucets and showerheads, plus spots on dishes that come out of the dishwasher.
Kettles collect scale quickly. Water heaters build up sediment at the bottom of the tank, which makes them work harder over time.
Soap and detergent need a little more to lather, and soap scum shows up in the tub.
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
At 131 mg/L most of the trouble is scale, and only a few things deal with it.
Ion-exchange water softener
The standard whole-house fix. It swaps calcium and magnesium for sodium or potassium and needs salt plus a drain. Size it with the calculator below.
Salt-free conditioner
No salt and no drain line. It changes how minerals form scale instead of removing them, so water still tests hard.
Reverse osmosis or carbon filter
Under-sink reverse osmosis removes minerals from drinking water only. Plain carbon filters improve taste but do not soften.
3 people × 75 gallons a day × 7.7 gpg = 1,724 grains a day. A 24,000-grain unit regenerates about every 13 days.
EPA record for Northbrook's water system
No health-based violations since 2016
Serves about 34,200 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 4
- Open now
- 0
EPA lists Northbrook as the system serving Northbrook. The hardness figure above comes from a different system's report, which TapWaterData uses for Northbrook.
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 Northbrook water hard?
Yes. It measures about 131 mg/L (7.7 grains per gallon), which the USGS classes as hard.
What is the water hardness in Northbrook in grains per gallon?
About 7.7 gpg. One grain per gallon equals 17.1 mg/L, so 131 mg/L divided by 17.1 gives 7.7.
What size water softener do I need in Northbrook?
For 3 people using 75 gallons each per day, 7.7 gpg works out to about 1,724 grains a day. A 24,000-grain softener covers that with a regeneration about every 13 days.
Has the Northbrook water system had EPA violations?
EPA records show no health-based violations for Northbrook since 2016. There were also 4 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- Deerfield135 mg/LHard
- Glenview229 mg/LVery hard
- Wheeling132 mg/LHard
- Winnetka135 mg/LHard
- Highwood120 mg/LModerately hard
- Lincolnshire380 mg/LVery hard
- Morton Grove229 mg/LVery hard
- Wilmette138 mg/LHard
- Mount Prospect112 mg/LModerately hard
- Buffalo Grove154 mg/LHard
Hardness data: TapWaterData US Water Hardness (utility report, July 28, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.