Why chlorine is in the water

Chlorine is a disinfectant. It's added on purpose to control germs in miles of pipe between the treatment plant and your home. EPA's legal limit for chlorine is 4 ppm; at levels above that, EPA lists eye and nose irritation and stomach discomfort.

What TTHM and HAA5 are

When chlorine meets natural material in water, it forms by-products. The two groups the law limits are total trihalomethanes (TTHM, limit 80 ppb) and haloacetic acids (HAA5, limit 60 ppb). Compliance is judged on running annual averages at each sampling location, so one high sample doesn't by itself mean a violation.

For reference, EPA lists these possible effects from drinking water above the limit over many years: for TTHM, liver, kidney, or central nervous system problems and an increased risk of cancer; for HAA5, an increased risk of cancer.

Joliet's results

  • TTHM: 2 ppb against an 80 ppb limit.
  • HAA5: 3 ppb against a 60 ppb limit.
  • Far below the 60 ppb legal limit.

What reduces them

  • Chlorine taste and smell: a carbon filter. A whole-home carbon system does it at every tap (NSF/ANSI 42).
  • TTHM: only filters certified for VOC reduction under NSF/ANSI 53 — which includes TTHM — or an RO system with that claim. Check the listing for "VOC reduction."
  • Not a softener: a water softener doesn't reduce chlorine or its by-products.

See whole-home carbon and under-sink reverse osmosis, or compare every system in the filter table.

Quick questions

Is chlorine in Joliet water a problem?

Chlorine is added on purpose to kill germs in the pipes, and the legal limit is 4 ppm. The most common complaint is taste and smell, which a carbon filter reduces.

Does a water softener remove TTHM?

No. A softener removes hardness minerals. Reducing TTHM takes a filter certified for VOC reduction under NSF/ANSI 53 or an RO system with that claim.

Sources

  1. City of Joliet 2025 Drinking Water Quality Report (published June 2026) — City of Joliet
  2. National Primary Drinking Water Regulations — U.S. EPA

This guide is general information, not medical or legal advice. Joliet Water Filtration is an independent business and is not affiliated with the City of Joliet. Product certifications are model-specific and can change; check the current listing before you buy.