Hard water in Caldwell, ID
County estimate from 531 water samples in Canyon County · July 2026
- ID typical
- 118 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- County estimate
Water samples from around Caldwell put hardness at about 170 mg/L (9.9 gpg), which would be hard on the USGS scale. Treat this as a rough guide: it is the median of 531 samples taken across Canyon County, mostly wells and streams, not a test of Caldwell's treated tap water.
At 170 mg/L, Caldwell is 52 mg/L above the typical Idaho figure of 118. Of the 10 nearest cities we track, 8 have softer water and 1 has harder. The range nearby runs from 86 mg/L in Meridian to 400 in Twin Falls.
What 170 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 170 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 × 9.9 gpg = 2,236 grains a day. A 24,000-grain unit regenerates about every 10 days.
EPA record for Caldwell's water system
No health-based violations since 2016
Serves about 78,740 people from groundwater.
- Health-based
- 0
- Monitoring or reporting
- 94
- Open now
- 1
EPA lists this system as serving Caldwell.
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 Caldwell water hard?
Yes. It measures about 170 mg/L (9.9 grains per gallon), which the USGS classes as hard.
What is the water hardness in Caldwell in grains per gallon?
About 9.9 gpg. One grain per gallon equals 17.1 mg/L, so 170 mg/L divided by 17.1 gives 9.9.
What size water softener do I need in Caldwell?
For 3 people using 75 gallons each per day, 9.9 gpg works out to about 2,236 grains a day. A 24,000-grain softener covers that with a regeneration about every 10 days.
Has the Caldwell water system had EPA violations?
EPA records show no health-based violations for Caldwell City of since 2016. There were also 94 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- Nampa170 mg/LHard
- Star124 mg/LHard
- Eagle90 mg/LModerately hard
- Meridian86 mg/LModerately hard
- Kuna90 mg/LModerately hard
- Garden City90 mg/LModerately hard
- Boise City90 mg/LModerately hard
- Twin Falls400 mg/LVery hard
- Lewiston122 mg/LHard
- Moscow111 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (county estimate, July 4, 2026), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.