Frequently Asked Questions

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Water hardness

What is Hard Water?

Hard water is a serious problem, and it is a common one. Water in 85% of the United States is so hard it should be softened to be of maximum usefulness. Hard water measures from 1 gpg (grains per gallon) to well in excess of 100 gpg. The Environmental Protection Agency recommends using water not exceeding 7 gpg.

There are only a few areas where water is sufficiently soft to be satisfactory for most homemaking needs. No natural water supply is completely free of hardness.

Communities that draw water directly from snow-filled mountain streams enjoy nearly ideal water in terms of a low amount of hardness.

New York City with supplies of one to three grains of hardness per gallon has relatively soft water. Still there are industries which must have water free of hardness materials. Some laundries in the area, for example, have found that zero soft water provides substantial soap savings.

The hardness of water supplies in this country ranges from 1 to 350 gpg (17.1 to 5985 mg/l).

gpg (grains per gallon). This is the most common method of designating the hardness of a water supply in our industry. Grains per gallon equals the number of grains of a given substance in one U.S. gallon of water. One grain equals 1/7000 pound and one U.S. Gallon of water weighs 8.33 pounds.

Hardness can also be expressed in terms of parts per million (ppm) or milligrams per liter (mg/l). However, because of high amounts of hardness in water, it is generally easier to express hardness in terms of grains per gallon. Conversion of parts per million or milligrams per liter into grains per gallon is quite simple. Simply divide the parts per million (or milligrams per liter) by 17.1 to convert to grains per gallon.
   Parts per million
(milligrams per liter) = Grains per gallon

Here is what an analysis in grains per gallon or parts per million means to you, according to the U.S. Department of the Interior and Water Quality Association standards:


grains per gallon
  milligrams per liter
parts per million

less than 1.0
1 to 3.5
3.5 to 7.0
7.0 to 10.5
10.5 and over
less than 17.1
17.1 to 60
60 to 120
120 to 180
180 and over
slightly hard
moderately hard
very hard

Most waters possess hardness minerals in amounts from 3 to 50 gpg (51.3 to 855 mg/l). Unfortunately, where water is extremely hard, the problem is often compounded by the presence of other contaminants such as iron and manganese.

Most people are quite aware that a water containing 15 to 30 grains (256.5 to 513 mg/l) of hardness minerals is definitely hard and difficult to use.

On the other hand, many people will tolerate a 5 grain (85.5 mg/l) water that is very objectionable to anyone accustomed to using completely soft water.

Why Does Hard Water Constitute a Problem?

Actually hardness is a source of many problems. One important trouble area is the way hardness minerals react with soaps and detergents.

So important is this aspect of the hardness problem that hardness is sometimes defined as "the effect of certain elements which combine with soap to form an insoluble material known as curd."

The list of elements that possess this property of hardness include iron, copper and manganese, all present normally in relatively small quantities. More common, of course, are calcium and magnesium, which are usually present in significant amounts. Clothes washed in zero soft water are free of troublesome hard water soap curd. For the homemaker water hardness makes home cleaning operations more difficult.

In the laundry, hard water leaves soap curd and detergent deposits on fabrics. This dulls colors and gives a gray or yellow appearance to white fabrics. Also hard water soap curd clings to fabric fibers, causing threads to become brittle and shortening the life of the material.

  • Hard water wastes soap and synthetic detergents.
  • Hard water leaves unsightly soap scum rings in the bathtub.
  • Hard water spots and streaks glassware and dishes.
  • Hard water builds up scale deposits in all water-using appliances, clogs hot water pipes.
  • Hard water hampers good grooming efforts
What is Hard Water Scale?

Scale is one of the most serious problems caused by hardness mineral deposits. This particular byproduct of water hardness puts many water-using appliances out of service. It clogs hot water pipes and can sharply reduce the heating efficiency of a boiler or water heater. When hard water is heated, scale is formed. This is due to (1) the breakdown of calcium and magnesium bicarbonates, (2) their reversion to the highly insoluble carbonate forms, (3) their precipitation from the water, and (4) their concentration on the interior surfaces of the water heater.

Under certain conditions the deposits form sludges. Both sludges and scale can lead to a sharp reduction in operating efficiency.

How Does Soft Water Save Energy?

In a University study, energy consumption of gas and electric water heaters operated and tested on hard water supplies was measured and compared to measured energy consumption of gas and electric water heaters operated and tested on softened water supplies.

The gas heaters operated and tested on hard water consumed 29.57% more Btu's of energy than the gas heaters operated and tested on softened water for the same amount of energy delivered.

The electric heaters operated and tested on hard water consumed 21.68% more Btu's of energy than the electric water heaters operated and tested on softened water for the same amount of energy delivered.

It is not necessary to heat water to a high temperature to produce scale. Any increase above the original temperature of the water can cause lime scaling to occur.

Although no chemical reaction occurs which causes calcium sulfate to deposit when the water is heated, this hardness mineral is unusual as it is less soluble in hot water than in cold.

Hard water can also be troublesome in industry. In many industrial applications, however, not only must hardness be removed from the water, but all mineral content must be eliminated. Mineral deposits can cause serious difficulties in boilers, air conditioning systems, gasoline and diesel engine cooling systems.

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