New Hampshire runs as five working zones. Manchester and the Merrimack Valley corridor at 100-180 mg/L on Manchester Water Works Lake Massabesic-source surface supply. Nashua and the southern NH border-corridor at 120-200 mg/L on Pennichuck Corporation surface-and-aquifer-supplemented supply. Concord and the central NH corridor at 120-200 mg/L on Concord General Services Penacook Lake-source surface supply. Portsmouth and the Seacoast corridor at 100-180 mg/L on Aquarion Water Bellamy Reservoir-source supply with substantial coastal salt-aerosol overlay. The White Mountains and Lakes Region tourism-corridor at 120-260 mg/L on mixed municipal and aquifer supplies. Rural New Hampshire well-water through the Granite State backcountry at 160-340 mg/L on local aquifer and well-water systems.
HOW IT BREAKS DOWNsoft to moderate (regional gradient)
Most New Hampshire municipal supplies run softer than most operators outside the region expect for a New England state — surface-source treatment delivers moderate-to-soft chemistry across the populous southern corridor. White Mountains corridor high-elevation UV-accelerated IGU seal degradation is operational wildcard parallel to what Easton Giordano documents for the Colorado Front Range and what Easton covers for the New Mexico mountain corridor. Portsmouth pre-1800 heritage residential among the deepest in northern New England — operationally distinctive concentration. Salt-aerosol overlay on Seacoast corridor commercial-and-residential. Ski-corridor seasonal commercial through Bretton Woods, Cannon, Loon, Waterville Valley, Attitash, Wildcat, Mount Sunapee, Pats Peak, Crotched Mountain, Gunstock. Foliage-season commercial concentration October. Granite State no-sales-tax commercial concentration drives substantial border-corridor retail commercial. Winter exterior work effectively shuts down December through February statewide.
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 Hampshire 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 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.
The hardest water in North America — Phoenix, Las Vegas, West Texas, much of the limestone Midwest. At this concentration calcium carbonate precipitates out of any water that touches the glass and dries, so what you are looking at is essentially limestone, growing one molecular layer at a time. Tap water cannot be part of the final pass under any circumstance, including "just a quick rinse." Above roughly 300 mg/L, buying distilled by the gallon stops making economic sense against a DI filter or a pure-water pole system, and a residential owner cleaning their own glass twice a year is usually better served by a service that already owns one.
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 Hampshire the spread runs from Portsmouth at 140 mg/L to Rochester at 165 — a difference big enough that the same bottle of cleaner behaves differently in each.
This page is about New Hampshire's water and nothing else. For how cleaning actually works in New Hampshire across the year — climate, seasonal timing, the local contaminants, the housing stock — see the New Hampshire 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.