How hard is the water in Trenton, NJ?

Tap water hardness
80mg/L
4.7gpg
Moderately hard

Reported by Trenton Water Works · September 2025

NJ typical
80 mg/L
EPA health violations since 2016
20
Softener for 3 people
24k grain
Data
Utility report

Tap water in Trenton has about 80 mg/L of hardness, which is 4.7 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Trenton Water Works, dated September 2025.

Trenton on the hardness scale, with nearby cities
060120180240300360+NJ typical 80Hamilton Square: 50 mg/LHamilton Square 50Mercerville: 75 mg/LMercerville 75Yardville: 75 mg/LYardville 75White Horse: 80 mg/LWhite Horse 80Heathcote: 82 mg/LHeathcote 82Kendall Park: 82 mg/LKendall Park 82Dayton: 82 mg/LDayton 82Monmouth Junction: 99 mg/LMonmouth Junction 99Princeton: 100 mg/LPrinceton 100Princeton Meadows: 100 mg/LPrinceton Meadows 100Trenton 80mg/L as calcium carbonate060120180240300360+NJ 80Hamilton Square: 50 mg/LHamilton S. 50Mercerville: 75 mg/LMercerville 75Yardville: 75 mg/LYardville 75White Horse: 80 mg/LWhite Horse 80Princeton: 100 mg/LPrinceton 100Princeton Meadows: 100 mg/LPrinceton. 10080 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Trenton sits close to the typical New Jersey figure of 80 mg/L. Of the 10 nearest cities we track, 3 have softer water and 6 have harder. The range nearby runs from 50 mg/L in Hamilton Square to 100 in Princeton.

What 80 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

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

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for Trenton

3 people × 75 gallons a day × 4.7 gpg = 1,053 grains a day. A 24,000-grain unit regenerates about every 22 days.

Size it for your household

EPA record for Trenton's water system

Trenton Water Works · PWSID NJ1111001

20 health-based violations since 2016

Serves about 217,000 people from surface water.

Health-based
20
Monitoring or reporting
104
Open now
0
20162017201820192020202120222023202420252026Total trihalomethanes (TTHM)Surface Water Treatment RuleLead and Copper RuleHaloacetic acids (HAA5)'16'18'20'22'24'26Total trihalomethanes (TTHM)Surface Water Treatment RuleLead and Copper RuleHaloacetic acids (HAA5)
Each dot is one health-based violation, placed at the start of its compliance period.
Contaminant or ruleViolationsPeriodStatus
Total trihalomethanes (TTHM)a disinfection byproduct52018–2024Resolved
Surface Water Treatment Rulefiltration and disinfection42017–2021Resolved
Lead and Copper Rulecorrosion control and lead sampling72018–2021Resolved
Haloacetic acids (HAA5)a disinfection byproduct42017–2018Resolved

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 Trenton water hard?

Somewhat. It measures about 80 mg/L (4.7 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Trenton in grains per gallon?

About 4.7 gpg. One grain per gallon equals 17.1 mg/L, so 80 mg/L divided by 17.1 gives 4.7.

What size water softener do I need in Trenton?

For 3 people using 75 gallons each per day, 4.7 gpg works out to about 1,053 grains a day. A 24,000-grain softener covers that with a regeneration about every 22 days.

Has the Trenton water system had EPA violations?

EPA records show 20 health-based violations for Trenton Water Works since 2016, involving Total trihalomethanes (TTHM), Surface Water Treatment Rule, Lead and Copper Rule. There were also 104 monitoring or reporting violations, which are about late or missing tests and notices.

Nearby cities

All 227 cities in New Jersey

Hardness data: TapWaterData US Water Hardness (utility report, September 15, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.