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Water Hardness Information

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The Environmental Protection Agency (EPA) establishes standards for drinking water which fall into two categories — Primary Standards and Secondary Standards. Primary Standards are based on health considerations and Secondary Standards are based on aesthetics such as taste, odor, color, or corrosivity. There is no Primary or Secondary standard for water hardness. In fact, the National Research Council (National Academy of Sciences) states that hard drinking water generally contributes a small amount toward total calcium and magnesium human dietary needs (National Research Council, Drinking Water and Health, Volume 3, National Academy Press, Washington, D.C., 1980).

The hardness of water is referred to by three types of measurements: grains per gallon, milligrams per liter (mg/L), or parts per million (ppm). The table below is provided as a reference.

As of December 22, 2015 the Occoquan Forest Water System has been connected to the PWCSA-East system, which is supplied by the Frederick P. Griffith Jr. Water Treatment Plant operated by Fairfax Water.

Grains Per Gallon Milligrams Per Liter (mg/L) or Parts Per Million (ppm) Classification
Less than 1.0 Less than 17.1 Soft
1.0-3.5 17.1-60 Slightly Hard
3.5-7.0 60-120 Moderately Hard
7.0-10.5 120-180 Hard
Over 10.5 Over 180 Very Hard

 

 East and West Water Systems

Grains Per Gallon Milligrams Per Liter (mg/L) or Parts Per Million (ppm) Classification
3.5-7.0 60-120 Moderately Hard

 

Bull Run Mountain and Evergreen Water System

Grains Per Gallon Milligrams Per Liter (mg/L) or Parts Per Million (ppm) Classification
7.0-10.5 120-180 Hard

 

Hoadly Manor System

Grains Per Gallon Milligrams Per Liter (mg/L) or Parts Per Million (ppm) Classification
7.0-10.5 120-180 Hard
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