The Water Hardness Scale, and Why Your City May Not Publish One

The USGS bands

Hardness is measured two ways and you will meet both. Water utilities report milligrams per litre as calcium carbonate; the softener industry works in grains per gallon. One grain per gallon is 17.1 mg/L, so dividing a utility figure by 17.1 gives you the number a softener is actually sized against.

The USGS bands are:

• Soft — 0 to 60 mg/L, under about 3.5 grains per gallon.
• Moderately hard — 61 to 120 mg/L, about 3.5 to 7 grains per gallon.
• Hard — 121 to 180 mg/L, about 7 to 10.5 grains per gallon.
• Very hard — above 180 mg/L, above about 10.5 grains per gallon.

Most of the Wasatch Front sits in the very hard band. That is not a defect in the water — hardness is calcium and magnesium dissolved out of the limestone the water passes through, and it is a secondary contaminant, which means it is an aesthetic and nuisance issue rather than a health one.

What hardness actually does

Hardness minerals come out of solution when water is heated or evaporates. That is why the scale shows up first inside the water heater, then on fixtures, glass and tile. It also binds with soap instead of letting it lather, which is why hard-water households use more detergent and still see film. None of that is dangerous. All of it costs money slowly.

Why most Utah cities publish no hardness figure

Hardness is a secondary contaminant, so Utah's water quality report template does not require it. Most cities therefore leave it out, and the ones that do include it are going beyond what is asked of them.

There is a second reason, and it is the better one. Where a city blends its own wells and springs with purchased district water, hardness moves with the season and with which part of town you live in. A single citywide figure would be misleading even if one existed. Bountiful publishes a 15 to 32 grain range for exactly this reason; Murray reports an 11.4 average against a 4.7 to 27.1 range across its sources.

So if your city publishes nothing, that is normal, and anyone quoting you a precise grain count for a city that does not publish one got it from a competitor's page rather than from the city.

How to read your own report

Your utility publishes an annual Consumer Confidence Report, usually as a PDF on the city or water district website. Look for a line reading hardness, total hardness, or calcium carbonate. If it is in mg/L, divide by 17.1 for grains per gallon. If the report gives a range rather than a single value, the high end is the number to size against, because a softener that is undersized for the hard months will let hardness through in those months.

If there is no hardness line at all, the only number that means anything is the one measured at your own tap. That is what a water test is for, and ours is free.

Sizing follows from the number

A softener is rated in grains of capacity between regenerations. The arithmetic is simple: your hardness in grains per gallon multiplied by the gallons your household uses per day gives the grains it has to remove daily, and the capacity divided by that figure gives roughly how many days it runs between regenerations. The EPA puts average family use at more than 300 gallons a day, which is the figure we use for a first estimate before measuring anything.

Two households at the same hardness can still need different systems, because use, iron content and whether anyone wants softened water at the kitchen tap all change the answer. That is why we measure before we quote.