By Ronald E. Hermanson, P.E.

Water is a good solvent and picks up impurities easily. Pure water—tasteless, colorless, and odorless—is often called the universal solvent. Rainwater and water in the topsoil, when combined with carbon dioxide to form very weak carbonic acid, make an even better solvent.

As water filters through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most important minerals that make it "hard." The degree of hardness, measured as grains per gallon, becomes greater as the calcium and magnesium content increases. Water with less than 3.5 grains of hardness per gallon is not considered hard.

This is the American Society of Agricultural Engineers water hardness classification system:

• Soft—0 to 3.5 grains per gallon
• Moderate—3.5 to 7
• Hard—7 to 10.5
• Very Hard—more than 10.5

 Hard Water Problems

The amount of hardness minerals in water determines the amount of soap and detergent necessary for cleaning. Excessive minerals form a sticky curd or deposit a film, such as bathtub ring, when soap is added to water. Removing this requires greater amounts of soap, detergent, cleaning compound, shampoo, and time. The hardness precipitate lodges in fabric after washing and makes it stiff and rough. Unremoved soil causes the graying of white fabric and the loss of brightness in colors.

Both bathing and grooming with soap in hard water leave a film of sticky soap curd on the skin. The film may prevent removal of soil and bacteria. Soap curd interferes with the return of the skin to its normal, slightly acid condition, and it may lead to irritation and infection. Soap curd on the hair makes it dull, lifeless, and difficult to manage.

Synthetic dishwater detergents are less effective in hard water because the active ingredient is partially inactivated by hardness, even though it stays dissolved. The alkaline builders, added to the detergent mixture to cut greases and oils, reacts with these greases and oils to form soap, which in turn produces soap curd in hard water. The deposits protect soil and bacteria and interfere with thorough cleaning.

Hard water also contributes to inefficient and costly water heater operation. Heated hardwater forms a scale that is a major cause of water heater failure. Since hard water scale is a poor conductor, heat is not transmitted to the water as rapidly as it is applied. The fuel wasted by poor heat transference increases hot water costs, and higher metal temperature leads to premature failure.

Furthermore, pipes clogged with scale reduce water flow and ultimately must be replaced. Fortunately, hard water problems can be solved by installing a water softener.

 Water Softening

A home water softener uses ion exchange to treat hardness minerals. An ion-exchange unit consists of a tank containing a sand-like, water-softening material commonly called sodium zeolite. The zeolite does not dissolve in water, but when hard water is passed through it, sodium ions from the zeolite are exchanged for the calcium and magnesium ions in the water. For this reason, zeolite is also known as an exchange material. After the zeolite has exchanged its supply of sodium for calcium and magnesium, it must be recharged.

Zeolite is recharged by passing a concentrated, salt brine solution through it. Zeolite releases calcium and magnesium ions and exchanges them for sodium ions from the salt. After flushing the excess salt and the calcium and magnesium released from the zeolite, the water softener is ready for use. Salt used to recharge zeolite is free of dirt and insoluble material to make it more efficient.

Most water softeners use either a timer or a hardness sensor to automatically start the recharging or regeneration process. You must add salt to the brine tank periodically to insure a constant supply of soft water.

Most soft water is used in the bathtub, lavatory, kitchen sink and laundry. Unsoftened water to the supply lines of toilets and outside faucets reduces the cost of softening. It is more efficient to soften cold water going to designated fixtures and to the hot water heater.

 Sizing

Companies that sell water conditioning units analyze water for hardness to determine correct softener size. A softener should have enough capacity to last at least three days between regenerations. A softener rated at 20,000 grains of hardness exchange capacity softens 1000 gallons of water with 20 grains hardness per gallon, or 2000 gallons with 10 grains per gallon before it needs regeneration. An average family uses about 50 gallons per person per day for all home water use (about 35 gallons per person per day must be softened if hard water is supplied to toilets).

Assuming a family of four uses 50 gallons per person, water hardness is 20 grains per gallon and all water is to be softened, then 4 persons x 50 gallons per person per day x 20 grains per gallon equals 4000 grains per day to be removed. To regenerate every third day, the water softener capacity must be 4000 grains per day x 3 days, or 12,000 grains minimum softener capacity.

In some areas, a water-softening service can be rented monthly. A service company owns the equipment and periodically delivers a freshly charged softener tank to replace the old one. The used tank is regenerated at a central plant and recycled.

 Iron Presence

Iron bacteria and oxidized iron clog a water softener not equipped with a green sand filter or another ion-exchange device installed ahead of the softener. The amount of dissolved iron a softener removes depends on water quality, regeneration type and backwashing controls, and the type of ion-exchange material. Follow manufacturer recommendations carefully because the removable iron amount may differ from model to model. An automatic softener makes frequent and thorough backwashing essential. Special salt or chemicals added to the regular salt helps prevent iron fouling of the softener media.

Oxidized iron clogs softeners. An offset pressure tank with an air-water separator installed before the softener reduces this oxidation. Water supplied to toilets and other fixtures should be treated if it contains iron or manganese because they stain fixtures if present in large quantities.

 Caution

People suffering from heart, kidney, or circulatory ailments should not drink home-softened water. Unsoftened drinking and cooking water supplied to the kitchen sink maintains a sodium-free diet and provides a source for those who prefer the taste of hard water. For more information obtain a copy of WSU publication, Sodium Content of Your Drinking Water, EB1525.

The best treatment method results from careful consideration of such factors as economics, water quality characteristics, water end-use, water temperature variances, and the inherent limitations of treatment technology. Consult local water treatment representatives before purchase and installation of any water treatment equipment.

Ronald E. Hermanson, Ph.D., P.E., Washington State University Extension Agricultural Engineer, Pullman.

Issued by Washington State Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Trade names have been used to simplify information; no endorsement is intended. Published May 1991. Subject code 376. A