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
Parts per million
(milligrams per liter) = Grains
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:
parts per million
1 to 3.5
3.5 to 7.0
7.0 to 10.5
10.5 and over
17.1 to 60
60 to 120
120 to 180
180 and over
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