Moderately hard across most of the state on a patchwork of surface and groundwater supplies; the pre-war housing stock and the spring pollen calendar are bigger working considerations than the water.
HOW IT BREAKS DOWNmoderate
New Jersey is a patchwork of surface-water and groundwater supplies, served by a mix of large investor-owned utilities (American Water, Suez/Veolia, Aqua), municipal providers, and private wells in the less-developed counties. North Jersey on the Wanaque and Newark reservoir systems runs 90-130 mg/L. Central Jersey on the Delaware Raritan canal and the Round Valley reservoir runs 110-180. South Jersey on the Cohansey-Kirkwood aquifer runs 130-220, and the southern Pine Barrens private wells can run softer than the municipal because the aquifer is naturally low-mineral in the sand-dominant zones. The state has no extreme of either softness or hardness; the water is uniformly workable. The dominant working considerations are the pre-war housing stock in the older Northeast Corridor towns and the heavy seasonal pollen calendar of the mid-Atlantic hardwood forests.
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.
New Jersey 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 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 a service-area typical for the named utility. Within New Jersey the spread runs from Newark at 95 mg/L to Cherry Hill at 180 — a difference big enough that the same bottle of cleaner behaves differently in each.
This page is about New Jersey's water and nothing else. For how cleaning actually works in New Jersey across the year — climate, seasonal timing, the local contaminants, the housing stock — see the New Jersey 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.
USGS national hardness survey data and utility Consumer Confidence Reports, 2023 vintage. City figures are service-area typicals for the named utility, not readings from any one tap. State ranges are the lowest and highest typical municipal values across the state, so they bracket the populated area rather than describing an average resident. Where a state blends sources seasonally, the range is wider than any single address will ever see.
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.