Three distinct profiles divide the state. Memphis pulls from the Memphis Sand aquifer and runs soft. Metro Nashville pulls the Cumberland River, moderately hard, while Williamson County and the Middle Tennessee suburbs pull karst-aquifer water. Knoxville on the Tennessee River is moderately hard and Chattanooga soft to moderately hard; smaller mountain-top East TN systems run their own sources.
HOW IT BREAKS DOWNsoft (Memphis); moderately hard (Clarksville, Knoxville, Nashville, Chattanooga)
The Metro-Nashville to Williamson County water-hardness jump is a protocol boundary. Memphis runs Memphis Sand aquifer soft with very low iron. Williamson, Rutherford, Wilson, Sumner County karst-aquifer systems publish no figure the site uses and carry sub-micron suspended particulate that resists standard acidic lift. Knoxville publishes moderately hard and Chattanooga soft to moderately hard on Tennessee River supply. Lookout Mountain and smaller East TN well systems publish no figure; test first. The Williamson County citric-prerinse protocol is mandatory; the Metro-Nashville protocol does not port.
A blended system means hardness moves with the blend. Two addresses on the same utility can read differently, and the same address can read differently across a year, depending on which source is carrying the load that season.
Tennessee spans 3 hardness bands, which means there is no single answer for the whole state — the method changes as you move across it. Both ends are below.
Tap water is clean enough to be the last thing that touches the glass. Wash with it, rinse with it, squeegee it off, and nothing measurable is left behind when it dries. No distilled rinse, no deionized final pass, no spot-free rinse aid — the mineral load is too low to precipitate anything you would see. The failure mode at this end of the scale is not water chemistry, it is technique: streaks here come from a worn rubber, a dirty edge, or a pass that dried before it was pulled.
Tap water is still fine for most residential glass, with two exceptions worth knowing. Dark glass shows a faint mineral haze that lighter glass hides, and glass that is hot enough to flash the water off before you pull the squeegee will spot regardless of how soft the supply is. On both, a distilled final rinse costs about a dollar a window and removes the variable entirely. Everywhere else at this level, the water is not what is wrong.
This is the band where the water starts writing on the glass. Wash with tap — the surfactant holds the minerals in suspension while you work, so the wash pass is not the problem — then rinse with distilled and pull that. The rinse is the whole intervention: it replaces the mineral-bearing water sitting on the glass with water that has nothing in it to leave. This single change resolves most of the "I cleaned it and it still looks bad" complaints in this range, and it does not require buying a system.
Hardest first — the order that matters, because the hard end is where the method has to change. Each figure is the named utility's own published number; cities whose utility publishes none are listed after them, without a band. Within Tennessee the spread runs from Memphis at 12–130 mg/L to Clarksville at 78–132 mg/L — a difference big enough that the same bottle of cleaner behaves differently in each.
Where Tennessee's city pages sit in the national city rankings: hardness rank out of 185 cities whose utility publishes a figure, dissolved-solids rank out of 100, the disinfectant each utility reports, and the months each city's cleaning calendar marks for a wash. Rank 1 is the hardest or most mineral-heavy.
| CITY | HARDNESS RANK | TDS RANK | DISINFECTANT | WASH IN |
|---|---|---|---|---|
| Clarksville | 110 / 18578–132 mg/L | not ranked | free chlorine | Jun, Oct |
| Knoxville | 112 / 18591 mg/L | 62 / 100150 mg/L | free chlorine | Jun, Oct |
| Nashville | 121 / 18562–113 mg/L | 66 / 100146 (range 128–189) mg/L | free chlorine | Jul, Oct |
| Chattanooga | 129 / 18554–90 mg/L | 88 / 10085 (range 76–94) mg/L | free chlorine | May, Oct |
| Memphis | 150 / 18512–130 mg/L | not ranked | free chlorine | Jun |
This page is about Tennessee's water and nothing else. For how cleaning actually works in Tennessee across the year — climate, seasonal timing, the local contaminants, the housing stock — see the Tennessee cleaning guide.
For a figure at your own address rather than your city, the Hard Water Scorer takes a ZIP code. If you run a pure-water system, the TDS diagnostic reads the other end of the same problem.
Each covered city utility's own published figure, taken from its most recent annual water quality report (Consumer Confidence Report) or its water-quality page, read in 2026. A city figure is the one its utility publishes for the service area, as a single number or the range it reports; it is not a reading from any one tap. A state range runs from the lowest to the highest figure published by the utilities we cover in that state, so it brackets those cities rather than describing an average resident. A state where no covered utility publishes a figure shows a planning estimate, labelled as one.
Private wells are outside all of it. A well is whatever the rock under it says, and the only number that describes one is a test of that tap. Have a reading that disagrees with this table? Send it to us — a number that contradicts the table is worth more than one that confirms it.