Tap Water Hardness, pH and Chloramine in Large US Cities: Data for Fishkeepers

What are the main findings?

Each point can be quoted on its own.

• 12 of 22 cities in AquaCompat's dataset of large US water systems disinfected with chloramine in 2025: Los Angeles, Houston, Philadelphia, San Diego, Dallas, Fort Worth, Austin, Indianapolis, San Francisco, Denver, Washington and Boston.
• The US Environmental Protection Agency says more than one in five Americans use drinking water treated with chloramines (EPA web page updated March 2026).
• In EPA's UCMR 3 monitoring, 2013–2015, 54.5 percent of sampling locations in large surface-water systems serving more than 100,000 people reported chloramine use at some point, against no more than 17.2% of ground-water sampling points in any size class.
• New York and Charlotte had the softest city tap water in the dataset in 2025, averaging 32 mg/L as CaCO3, or about 1.8 dGH.
• Indianapolis had the hardest tap water among cities that print an average, 317 mg/L as CaCO3, or about 17.8 dGH, in 2025.
• By US Geological Survey hardness classes, the 2025 figures give 2 soft, 4 moderately hard, 5 hard and 5 very hard cities (of 16 with a hardness figure).
• 6 of 22 cities printed no hardness figure in their 2025 report, and only 11 of 22 cities printed a pH value or range.

Does my city use chlorine or chloramine?

Check the table: in 2025, 12 of 22 cities in this dataset named chloramine as the disinfectant in their pipes, and 9 of 22 cities named chlorine. San Jose Water says chloramine and chlorine may both be present, depending on the source reaching a neighbourhood. Chloramine is chlorine combined with ammonia, and EPA explains that utilities use it because it lasts longer in the pipes.

Three entries need a footnote. Houston's figures are for its Main System; smaller Houston systems list chlorine. DC Water switches to chlorine alone for a short period each spring. Dallas's report lists only total chlorine, so its chloramine entry comes from the utility's web page, as Denver's comes from the Denver Water FAQ.

Why does chlorine versus chloramine matter for an aquarium?

It decides which treatment works. UF/IFAS Extension describes free chlorine as something vigorous aeration can drive off in about 24 hours, while chloramine survives aeration and has to be neutralised chemically. Breaking chloramine apart also frees ammonia, so the conditioners that bind ammonia as well as chlorine suit anyone in the chloramine column above.

A common misreading is that leaving a bucket to stand overnight makes any city's tap water safe. That works only where the report names chlorine, and even there the label can change: San Jose's supply is mixed and DC Water switches disinfectant each spring. Our step-by-step tap water treatment guide sets out the order of treating and testing.

How hard is tap water in big US cities?

Most big-city tap water is moderately hard to very hard: averages or range midpoints in the 2025 reports run from about 1.8 dGH in New York and Charlotte to about 17.8 dGH in Indianapolis. The chart converts each utility's figure to German degrees of general hardness (dGH), the unit aquarium test kits and species guides use.

Utilities report hardness in mg/L (or ppm) as calcium carbonate. The conversion factor is 17.848 mg/L as CaCO3 per dGH, so divide the report's mg/L figure by that factor; grains per gallon convert at 17.1 mg/L as CaCO3 per 1 grain per gallon. Total hardness in a utility report measures calcium and magnesium, which is what an aquarium GH test reads; the explainer on GH and KH covers how it differs from carbonate hardness (KH).

Why do some cities show a range instead of one hardness figure?

Because cities that blend several sources deliver different water to different neighbourhoods, and their reports print per-source or per-plant figures rather than one average. Los Angeles is the clearest case: Los Angeles Aqueduct water and local wells average roughly half the hardness of the water from the Metropolitan Water District's Weymouth and Diemer plants. Philadelphia's three plants, San Diego's plants and purchased water, and San Jose's mountain, valley and well sources work the same way. For those cities the chart's midpoint is only a rough centre, and the range shown in the next table is the figure to plan around. Supply can also change with the season: Las Vegas says some areas receive groundwater blended with Lake Mead water between April and October.

Which US cities have soft water and which have hard water?

Only New York and Charlotte have soft water by the USGS definition, while Phoenix, San Diego, San Jose, Las Vegas and Indianapolis have very hard water. USGS hardness classes are 0–60 soft, 61–120 moderately hard, 121–180 hard, over 180 very hard mg/L as CaCO3. Applied to the 2025 reports, that gives 2 soft, 4 moderately hard, 5 hard and 5 very hard cities (of 16 with a hardness figure). The second table converts the class boundaries to dGH.

Is "hard water" in a utility report the same as hard water for fish?

Not quite. The USGS scale calls anything above 120 mg/L as CaCO3 hard, which is under 7 dGH, while the German classification that many aquarium books follow uses these bands: <8.4 soft; 8.4–14 medium; >14 hard dGH (German WRMG 2007). Houston and Washington, both "hard" to the USGS, count as soft in German terms. Compare a species' dGH range with your city's dGH, not with the word in the utility report. Private wells are outside this dataset, and USGS found 60 percent of sampled domestic wells had hard water, so well owners should test.

What pH is tap water in large US cities?

Where it is reported, big-city tap water is close to neutral or alkaline, and San Francisco's is the most alkaline, averaging pH 9.3 in 2025. Only 11 of 22 cities printed pH at all, so the table below is short.

What does high tap water pH mean when the water is also chloraminated?

It makes the ammonia released from chloramine more dangerous. UF/IFAS Extension tables show that higher pH shifts total ammonia toward its toxic un-ionised form, with roughly ten times more of it at pH 8 than at pH 7 in warm water. San Francisco pairs chloramine with an average pH of 9.3, so an ammonia-binding conditioner matters more there than in soft, chlorinated New York. The aquarium pH guide explains how KH holds pH steady once the water is in the tank.

Which fish suit the tap water in your city?

Most popular community fish cope with the moderately hard water most large cities supply, but the softest and hardest cities rule some species out without water treatment. The table compares each species' published general hardness range, from the AquaCompat species fact base (Seriously Fish, Maidenhead Aquatics and other care sources), with each city's 2025 dGH figure. A city in the "above" column supplies water harder than the published range; "below" means softer.

How should fishkeepers use the species comparison?

Soft-water cities

New York and Charlotte, at about 1.8 dGH, suit soft-water tetras and rasboras straight from the tap: neon tetras (1–12 dGH), harlequin rasboras (1–12 dGH) and discus (0–8 dGH) all fit. The harlequin, chili and galaxy rasbora comparison sets out what the small rasboras tolerate. The same water is too soft for hard-water livebearers, and the fish that live well with guppies share that need for minerals.

Very hard cities

Indianapolis and Las Vegas averages fall inside the published ranges for mollies (15–25 dGH) and Lake Malawi cichlids such as the peacock (10–25 dGH) and yellow lab (10–25 dGH), which also want alkaline water (pH 7.5–8.5 for the peacock). Our tank mates for Malawi cichlids build on that base. Keeping discus there means softening the water first; the guide to RO and RO/DI water explains mixing reverse osmosis water with tap water to a target GH, and the companions that suit discus need the same soft water.

Shrimp

Crystal red shrimp (4–6 dGH) match only the Austin and Denver averages, while cherry shrimp (6–10 dGH) match the middle of the table from Columbus to Los Angeles. The Caridina versus Neocaridina shrimp breakdown explains the split, and tank mates for cherry shrimp follow the same moderate water.

A Philadelphia, Los Angeles or San Jose midpoint can sit inside a species range while a given address is well outside it, so test GH before buying fish, then check the community in the tank mate guides by species.

How many Americans get chloraminated tap water?

EPA puts the figure at more than one in five Americans: its chloramines page, updated March 2026, says that share of the population uses drinking water treated with chloramines.

EPA's UCMR 3 monitoring, 2013–2015, shows where chloramine is concentrated. At sampling points where water has spent longest in the pipes, 54.5 percent of sampling locations in large surface-water systems serving more than 100,000 people reported chloramine use at some point, against 9.7% at small ground-water systems. Large cities drawing from rivers and reservoirs are the most likely to chloraminate, which matches the city table.

How we built this data

AquaCompat read the Consumer Confidence Report (CCR), the annual water quality report every US community water system sends its customers, for the main utility in 22 of the largest US cities. The editions used cover calendar year 2025. A copy of each report was saved and every figure re-checked against it on 22 October 2026; the Dallas and Denver disinfectant entries also use each utility's water quality web page. National figures come from EPA's chloramines page and EPA-810-R-16-012, and hardness classes from USGS Water-Supply Paper 2254 (Hem, 1985). We did no water testing of our own.

Our calculations are simple.

• dGH is mg/L as CaCO3 divided by 17.848; Denver's figures, printed in parts per billion, were first divided by 1,000.
• Where a report printed only a range or per-source figures, the hardness table and chart use the simple midpoint of the lowest and highest values, labelled every time. It is not a measured average.
• Las Vegas prints one hardness figure for setting water softeners, used as printed.
• The species table compares each city's dGH with the GH ranges in AquaCompat's species fact files on 22 October 2026.

The data have limits.

• CCR averages vary by source, season and neighbourhood. Check your own utility's report, or test your tap.
• 6 of 22 cities print no hardness, and only 11 of 22 cities print pH; missing cells are left blank.
• Jacksonville and Nashville are missing because no report was collected. Oklahoma City was dropped because its report could not be stored for re-checking.
• Each city entry covers one utility; suburbs often buy water from a different system.
• UCMR 3 counts sampling locations from 2013–2015, not people, and some systems have changed disinfectant since.

How to cite this page

Use this citation, or link to this page next to the figure you use.

AquaCompat, "Tap Water Hardness, pH and Chloramine in Large US Cities: Data for Fishkeepers", updated 22 October 2026, https://aquacompat.com/data/tap-water-for-aquariums/.

The data, tables and charts on this page are free to reuse under a Creative Commons Attribution 4.0 (CC BY 4.0) licence, provided you credit AquaCompat with a link to this page. For a single city's figure, please also name that utility's water quality report.