Delaware splits cleanly by county. New Castle County's two covered cities run municipal systems, Wilmington on Brandywine Creek surface water that spans moderately hard to very hard across its published range. Kent County flips to City of Dover and Tidewater Utilities groundwater. Sussex coastal beach communities run Tidewater Utilities and smaller systems, with brackish-bay plus open-Atlantic salt aerosol defining coastal chemistry. Brandywine Valley well-water carries a Piedmont iron-clay fraction.
HOW IT BREAKS DOWNmoderately hard (Dover, Newark); hard (Wilmington); 2 of 5 covered cities publish no figure
New Castle County commercial protocols port from Baltimore I-95 logic. Kent County requires longer dwell times than Wilmington baseline. Sussex coastal is brackish-bay plus Atlantic salt aerosol with bay-side requiring roughly 1.3x ocean-side dwell time per window. Brandywine Valley estate residential is its own category — heritage glass, slow pacing, citric-protocol well-water chemistry. Veolia Water Delaware (formerly Suez) and Artesian Water serve New Castle County. City of Dover and Tidewater Utilities serve Kent County. Sussex coastal Tidewater Utilities plus smaller municipals.
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.
Delaware spans 4 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.
A distilled rinse stops being an improvement and becomes the method. Tap water left to dry on glass at this concentration deposits a visible film within minutes, and the film is cumulative: each cleaning that ends in tap water adds a layer that the next cleaning has to get through first. Glass on a sprinkler line or under a runoff drip needs a maintenance interval, not just a better wash — the deposit is arriving faster than a cleaning schedule built around dust would predict.
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 Delaware the spread runs from Newark at 68 mg/L to Wilmington at 94–228 mg/L — a difference big enough that the same bottle of cleaner behaves differently in each.
Where Delaware'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 |
|---|---|---|---|---|
| Wilmington | 40 / 18594–228 mg/L | not ranked | free chlorine | Aug, Oct |
| Dover | 125 / 18523–127 mg/L | 34 / 100275.1 (range 174–406) mg/L | free chlorine | Jul, Oct |
| Newark | 132 / 18568 mg/L | not ranked | free chlorine | Aug, Sep, Oct |
| Middletown | not ranked | not ranked | free chlorine | Jun, Sep, Oct |
| Smyrna | not ranked | not ranked | free chlorine | Jul, Oct |
This page is about Delaware's water and nothing else. For how cleaning actually works in Delaware across the year — climate, seasonal timing, the local contaminants, the housing stock — see the Delaware 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.