Does Miami Have Hard Water?
Short answer: Miami's source water is naturally hard, but most of it is softened before it reaches you. Miami-Dade Water and Sewer (WASD) draws mainly from the limestone Biscayne Aquifer; a USGS study of 189 wells found a median of 92 mg/L calcium and 3.7 mg/L magnesium, which works out to roughly 245 mg/L hardness (very hard) before treatment (USGS). WASD says its main plants use lime treatment to reduce hardness (WASD 2025 report), but its report does not list hardness at the tap, so the only way to know your number is to test.
The Biscayne Aquifer: Very Hard at the Source
The Biscayne Aquifer is a shallow limestone aquifer, and limestone is mostly calcium carbonate. A USGS study of water from 189 wells tapping the aquifer found it "predominantly a calcium-bicarbonate type," with these typical values (USGS WRI 91-4009):
| Constituent (untreated well water) | Median | Mean |
|---|---|---|
| Calcium | 92 mg/L | 94 mg/L |
| Magnesium | 3.7 mg/L | 5.3 mg/L |
| Bicarbonate | 272 mg/L | 283 mg/L |
| Dissolved solids | 350 mg/L | 379 mg/L |
| Calculated hardness as CaCO3 | about 245 mg/L (14 gpg) | about 257 mg/L (15 gpg) |
Calcium, magnesium, bicarbonate and dissolved solids from USGS Water-Resources Investigations Report 91-4009 (1991). Hardness is our calculation (calcium x 2.5 + magnesium x 4.1). This describes raw aquifer water, not treated tap water, and the data are decades old.
By the USGS scale (over 180 mg/L is very hard), untreated Biscayne Aquifer water is very hard. So untreated water drawn from the aquifer, including from private wells, can be expected to be hard, and WASD softens the water at its large plants. See our hardness scale for the classes.
Which Plant Serves You
WASD's 2025 report describes several supplies (WASD):
| Supply | Area (per WASD) | Source | Hardness Treatment | Disinfectant |
|---|---|---|---|---|
| Alexander Orr, Jr. plant (Main System) | South of SW 8 Street to about SW 264 Street | Biscayne Aquifer | Lime treatment to reduce hardness | Chloramine |
| Hialeah and John E. Preston plants (Main System) | Generally north of SW 8 Street to the Broward line | Biscayne Aquifer | Hialeah treated like Orr; Preston uses "enhanced softening" | Chloramine |
| Hialeah Reverse Osmosis plant | City of Hialeah and the County's NW service area | Upper Floridan Aquifer (brackish) | Reverse osmosis removes salts and ions | Chlorine |
| South Dade Water Supply System | South of SW 264 Street, unincorporated areas | Biscayne Aquifer | Report says "disinfected and stabilized"; no softening step described | Chlorine |
From the Miami-Dade WASD 2025 Water Quality Report. Small areas supplied by Homestead (Redavo) and North Miami Beach are covered in those cities' reports. If your water comes from a city utility rather than WASD, check that utility's report.
Two practical points follow. Homes on the Main System get water that has been lime-softened, so it should be noticeably less hard than the raw aquifer. Homes in the South Dade system get Biscayne Aquifer water for which WASD describes disinfection and stabilization but no softening step, so they may see harder water; test to find out.
Why You Should Test Your Own Tap
WASD's 2025 report lists 22 detected parameters, but hardness is not one of them, and its older reports we checked (2006 to 2015) also describe lime softening without giving a tap hardness number. Online figures for Miami hardness mostly come from equipment sellers and disagree with each other. So test your own water: hardness test strips give an answer in a minute, and our testing guide explains the numbers. You can also call WASD's water quality line listed in the report for your plant.
If your result is under about 120 mg/L (7 gpg), you probably do not need a softener; the Minnesota Department of Health uses that threshold for when one may help. Above it, see our water softener guide.
Chloramine vs Chlorine
The 2025 report lists chloramines for the Main System (average 2.5 ppm) and chlorine for the South Dade system (1.3 ppm average) and Redavo. The Hialeah RO plant adds chlorine. On the Main System, choose a drinking water filter with a chloramine claim, such as the 3M Aqua-Pure 3MDW301 (see our under sink guide). Shower filters certified to NSF/ANSI 177 cover free chlorine, not chloramine.
PFAS in Miami-Dade Water
The report's "additional contaminants" table shows PFAS monitoring under EPA's 2024 rule. For the Main System it lists PFOS at 33 ppt (range 7 to 33) and PFOA at 13 ppt (range 3 to 13); for South Dade, PFOS 32 ppt and PFOA 13 ppt. EPA's enforceable limit for both is 4.0 ppt, with compliance required from 2029 (or 2031 under a proposed extension) (EPA). The report notes these standards were recently promulgated and initial compliance monitoring is underway, so these results are not violations today.
If you want to reduce PFAS now, use a filter certified for PFAS reduction, such as the LARQ Advanced Under Sink Filter (NSF 53 total PFAS) or a Brita Elite pitcher on a budget. See best water filters for PFAS, including what today's certifications do and do not prove.
Lead, Sodium and Fluoride
- Lead: Main System 90th percentile 3.2 ppb, with 1 of 102 homes over the 15 ppb action level; South Dade 1.1 ppb, none over. WASD has submitted a lead service line inventory; the report points customers to miamidade.gov/knowyourpipes.
- Sodium: 33 ppm in the Main System and 27 ppm in South Dade, both well under Florida's 160 ppm standard. If you install a softener, it will add sodium in proportion to your hardness; see is softened water safe to drink?
- Fluoride: the three main plants stopped adding fluoride on June 6, 2025, following a County resolution and Florida Senate Bill 700. WASD says Main System levels since then range from 0.1 to 0.3 ppm from natural sources.
Best Fixes for Miami Homes
- Test first. Main System water is softened at the plant; you may not need a softener at all.
- South Dade and private wells: test hardness, iron and, for wells, have a certified lab check health contaminants. See our well water guide.
- Drinking water: PFAS is the bigger issue in the 2025 data than hardness. A certified PFAS filter or RO at the kitchen tap addresses it.
- Scale and spots: if you still see them, descale with vinegar or citric acid (limescale guide), and consider a softener only if your test shows hard water.
Check Hardness Test Strips on Amazon
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Frequently Asked Questions
Miami's source water from the Biscayne Aquifer is naturally very hard, around 245 mg/L based on USGS well data. Miami-Dade Water and Sewer lime-softens water at its main plants, but its 2025 report does not list tap hardness, so test your own tap.
WASD does not publish a tap hardness figure. Its main plants use lime treatment to reduce hardness, and the Hialeah reverse osmosis plant removes most dissolved minerals. Online figures vary widely, so a home test is the reliable answer.
Often not on the Main System, because WASD softens the water at the plant. Homes on the South Dade system or private wells are more likely to have hard water. Test first; above about 120 mg/L (7 gpg) a softener may help.
The Main System uses chloramine (2.5 ppm average in 2025). The South Dade system and Redavo use chlorine, and the Hialeah RO plant adds chlorine.
Yes. WASD's 2025 report lists PFOS at 33 ppt and PFOA at 13 ppt in the Main System during initial monitoring. EPA's limit for each is 4 ppt, with compliance due from 2029. A certified PFAS filter reduces exposure now.
Not since June 6, 2025. WASD stopped fluoridation at its three main plants under a County resolution and Florida Senate Bill 700. Natural levels are 0.1 to 0.3 ppm.
Last updated: October 2026. Sources: Miami-Dade WASD 2025 Water Quality Report, USGS WRI 91-4009, Biscayne Aquifer chemistry, USGS hardness, EPA PFAS regulation.