Chlorine taste and smell in tap water

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Why utilities add chlorine or chloramine

Every public water system has to keep water safe not only when it leaves the treatment plant but all the way to your faucet, sometimes days later and miles away. Utilities do that with secondary disinfection: a small, measured residual of disinfectant that stays in the pipes. In the U.S. that residual is either free chlorine or chloramine. EPA explains that chloramines are most commonly formed by adding ammonia to chlorine, provide longer-lasting disinfection as water moves through pipes, have been used by utilities since the 1930s, and are used by more than one in five Americans (EPA: chloramines in drinking water).

Both are regulated. The maximum residual disinfectant level (MRDL) is 4.0 mg/L, measured as chlorine, for either one. Utilities typically run well below that.

Chlorine vs chloramine at a glance

Which California utilities use which

Most large Southern California systems use chloramine, in part because the region relies heavily on imported water that travels long distances. Some groundwater-based utilities use free chlorine. From 2025 reports and official pages:

• Metropolitan Water District of Southern California, which treats imported Colorado River and State Water Project water for much of the region, says all five of its treatment plants use ozone as the primary disinfectant, then add chlorine and ammonia to form chloramines for the distribution residual (MWD water treatment).
• LADWP uses chloramines and reports ammonia plus chloramines of about 0.4 to 0.5 mg/L as N at its main supply points (LADWP 2025 report).
• City of San Diego uses ozone (Alvarado and Miramar plants) or chlorine dioxide (Otay plant) first, followed by chloramines. In 2025 it analyzed 7,691 distribution samples, averaging 1.75 mg/L (range not detected to 3.80) (San Diego 2025 report).
• Riverside Public Utilities, which runs on groundwater, reports a chlorine residual averaging 0.58 mg/L (range 0.25 to 0.85) (RPU 2025 report).

Your own utility's report will say "chlorine" or "chloramines (as Cl2)" in its disinfectant row. Enter your ZIP below to see which system serves you.

Other tastes and smells, decoded

• Earthy or musty: usually geosmin or 2-methylisoborneol (2-MIB), harmless compounds produced by algae in reservoirs, more common in warm months. San Diego's 2025 supplemental data list both in untreated reservoir water at parts-per-trillion levels; ozone treatment helps reduce them.
• Rotten egg: often hydrogen sulfide from a water heater or a drain rather than the utility supply. If only the hot water smells, start with the water heater.
• Metallic or bitter: can come from home plumbing, especially after water sits in pipes overnight. Run the cold tap until it feels colder before drinking, and see the lead section of your utility's report.
• Salty or mineral: high total dissolved solids and sodium, common with imported Colorado River water. See the hard water guide.
• Sudden strong chlorine smell: utilities sometimes raise the residual after main breaks or during maintenance. If it persists for days, call your utility.

How to reduce chlorine or chloramine taste

1. Chill it. Cold water tastes less of chlorine. A covered pitcher in the fridge also lets some free chlorine dissipate. This works much less well for chloramine.
2. Use a certified carbon filter. NSF/ANSI 42 covers aesthetic claims, including chlorine taste and odor and, separately, chloramine reduction. For chloramine, look for a product certified specifically for chloramine, often using catalytic carbon. Search the NSF listings by contaminant.
3. Consider reverse osmosis if you also want to reduce dissolved contaminants. RO systems include carbon stages that address disinfectant taste.
4. Change cartridges on schedule. A spent carbon filter stops removing taste and can let it come back suddenly.
5. Showers and whole-house: whole-house carbon systems exist, but chloramine needs more contact time than chlorine, so size the system for chloramine if that is what your utility uses.

When chloramine must be removed

Chloramine is safe to drink, but it is not safe for every use. LADWP's 2025 report reminds customers that people using dialysis machines must make adjustments to remove chloramines, and that fishponds, tanks and aquariums need treatment because chloramines can harm fish. Dialysis centers handle this routinely; home dialysis patients should confirm with their provider. Aquarium conditioners must say they neutralize chloramine, not just chlorine.

Disinfection byproducts: the trade-off

Disinfectants can react with natural organic matter to form byproducts. Two groups are regulated: total trihalomethanes (TTHM, limit 80 µg/L) and five haloacetic acids (HAA5, limit 60 µg/L), both judged on a running annual average. In 2025, San Diego's highest locational average was 55 µg/L for TTHM and 15 µg/L for HAA5, and Riverside's highest TTHM average was 6.1 µg/L. Using ozone first and chloramine for the residual is one way large utilities keep these byproducts down. A certified carbon filter also reduces many of them; check the certification for "TTHM" if that matters to you.

For the contaminants a carbon filter will not touch, see the guides on nitrate, arsenic and chromium 6.

Related guides

• Hard water in California
• PFAS in California drinking water
• Chromium 6 in California water
• Nitrate in California well and tap water
• Arsenic in California drinking water
• How to check tap water by ZIP
• City water guides
• Regional water guides

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