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Water Quality Answers

What is the classification of water hardness?

Most accepted classifications (including that of the Water Quality Association) are based on that of the U.S. Geological Survey.

A Charles H. Ullery paper presents a thorough assessment of water hardness classifications for the American Society of Agricultural Engineers. The ASAE Standard S-339 is:

soft: 0-3.5 grains per gallon (gpg),

moderate: 3.5-7.0 gpg,

hard: 7.0-10.5 gpg, and

very hard: over 10.5 gpg

This is identical to the USGS classification. WQA has added 0-1 gpg as soft and 1-3.5 gpg as slightly hard because discernable benefits can be realized when softening down to less than one gpg, and the recognized standard of acceptable performance for household water softeners has been established at less than one gpg.

Mr. Lee Johnston of the American Institute of Laundering has reported the costs of laundry operations almost double on five gpg water as opposed to water softened to less than one gpg. The Benjamin Franklin Hotel in Philadelphia has documented several benefits with softening five to nine gpg water to less than one gpg: e.g., linen life doubles, soap consumption drops, washing times decrease, and boiler downtimes appreciably decrease. The National Association of Institutional Laundry Managers has estimated 10% savings in linens when softening water of two gpg to less than one gpg, and 18% savings when softening water of four gpg to less than one gpg. The Ohio Agricultural Experiment Station studied cost, cleaning time, and water use savings that were positively documented for 19 families in a water softening study. Benefits were found for families that had incoming water hardness of less than five gpg.

Each grain per gallon of water hardness contributes its share to the woes of calcium and magnesium in water. The level that is acceptable or preferred is really a matter of an individual’s specific need or personal desire. The Betz Handbook of Industrial Water Conditioning perhaps said it best in paraphrasing: "one accustomed to using a water with less than 50 ppm of hardness may call waters with a hardness of 100 ppm rather hard." The referenced Water Quality Criteria from the California State Water Pollution Control Board shows a number of processes, such as laundering, equipment washing, food processing, and boiler feedwater, where the recommended water hardness is zero to three gpg.

Wednesday,February 23, 2000 at 11:31 AM