Key West Water Hardness & Quality Report (2026)
Water Hardness
15.8 grains per gallon
Source
groundwater
pH Level
8.5
neutral = 7.0
Lead
0.007 mg/L
✓ Below action level
TDS
843.6 mg/L
Est. Daily Cost
$0.72
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In Key West, your appliances are currently losing 36% efficiency due to mineral buildup.
| Appliance | In Key West | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 1.5 yrs | 8.5 yrs | -82% |
| Washing Machine | 3.6 yrs | 12 yrs | -70% |
| Water Heater | 5 yrs | 15 yrs | -67% |
Regional Water Comparison
How Key West compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Key West, Florida | 270 mg/L | 11 ppt | 🔴 Very Hard | groundwater |
| Marco Island, Florida | 269.5 mg/L | 11 ppt | 🔴 Very Hard | groundwater |
| Marco, Florida | 269 mg/L | 11 ppt | 🔴 Very Hard | groundwater |
| Florida City, Florida | 272 mg/L | 11.1 ppt | 🔴 Very Hard | groundwater |
| East Naples, Florida | 106.5 mg/L | 5.9 ppt | 🟡 Moderately Hard | groundwater |
National Benchmark
How Key West compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Key West | 270 mg/L | 🔴 High |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Key West's Water Unique?
Local geology and source profile
Key West, Florida, in Monroe County at the southernmost tip of the continental United States, receives virtually all of its drinking water from the mainland — piped approximately 130 miles through the Florida Keys Aqueduct Authority (FKAA) transmission system. The water originates from wellfields in Florida City, Miami-Dade County, drawing from the Biscayne Aquifer — a shallow, highly productive aquifer underlying South Florida. From Florida City, treated water travels through a single transmission main running the length of the Overseas Highway to reach Key West, making it one of the most geographically isolated municipal water supply systems in the continental United States.
The very hard 270 mg/L water is a product of the Biscayne Aquifer's unique carbonate geology. This aquifer is hosted within the Miami Limestone and Fort Thompson Formation — Pleistocene-age carbonate rocks formed from ancient coral reefs, ooids, and shell deposits that accumulated when South Florida lay beneath a warm, shallow tropical sea. These porous, highly soluble limestone formations dissolve calcium carbonate readily into percolating groundwater. As water travels through the FKAA transmission main across the Keys — resting atop the Key Largo Limestone, another ancient reef complex — additional mineral contact occurs before reaching residential taps.
At 270 mg/L, Key West water is very hard — among the highest hardness levels for any Florida Keys community. Residents face aggressive scale deposition on all fixtures: kettles accumulate thick white crust within weeks, showerheads clog rapidly, and glass shower doors develop heavy calcium film requiring frequent treatment. Water heaters in the tropical climate face compound stress from scale and saltair humidity. A whole-house water softener is strongly recommended, particularly for protecting appliances and plumbing fixtures. Under-sink reverse osmosis for drinking water is also widely used among Key West residents given the combination of high hardness, elevated TDS of 843.6 mg/L, and PFAS concerns.
Geology & Source: Key West is supplied via the Florida Keys Aqueduct Authority transmission main drawing from the Biscayne Aquifer in Miami-Dade County — hosted in Pleistocene Miami Limestone and Fort Thompson Formation ancient coral reef and oolitic carbonates — highly soluble reef rock dissolves calcium carbonate readily, producing very hard water at 270 mg/L.