UNIVERSITY PARK, Pa. -- Everyone knows the difference between software and hardware or softball and hardball, but some consumers are hard pressed to remember exactly what softened water is, says an engineer in Penn State's College of Agricultural Sciences.

"For most people, their definition of hard and soft water is based on whether the water leaves a detergent film on pots and fixtures or whether the water makes their hair more silky and manageable," says Paul Robillard, associate professor of agricultural engineering.

Robillard explains that water labeled "soft" or "hard" depends solely upon the levels of two soluble minerals -- calcium and magnesium -- in the water. "From a health standpoint, calcium and magnesium have no adverse affects," he says. "Both minerals are essential daily nutrients and along with other minerals often give drinking water the fresh taste many consumers want."

If calcium and magnesium are at high levels, the minerals will build up on surfaces such as plumbing pipes, eventually plugging them. Minerals also can damage hot water heaters and make laundry detergents less effective.

Engineers measure water hardness by calculating how much calcium carbonate is dissolved in the water. A measurement of less than 1 grain per gallon or 17 parts per million means that the water supply is soft. Robillard offers a table of hard water values:

"If you have your water tested, the report will use one or both of those values to determine how hard the water supply is," Robillard says. "Once you determine the hardness level of the water, you either can live with it or treat the water to reduce the mineral content."

Water can be softened by a process called ion exchange. Ion exchange works by filtering water through a synthetic or natural sand-like material called resin or zeolite. The resin is coated with positively charged sodium ions. As water flows through the unit, the resin exchanges its sodium ions for the positively charged calcium and magnesium ions. When the resin has absorbed its capacity in hardness minerals, the water softener must regenerate its ion exchange capacity.

"Regeneration works by backwashing the resin with a brine solution that flushes out the calcium and magnesium ions," Robillard explains.

--Kinds of softeners. Robillard says most homeowners can choose between softeners that have programmable regeneration timers or demand-control models outfitted with regeneration sensors. "Timer models work best for households that have regular water use cycles, but they can waste water and salt because they regenerate whether the resin needs it or not," he says.

--Maintenance. All water softeners require regular maintenance to function properly. The resin can develop bacteria or fungi, or become clogged with mud. Iron deposits can clog the resin as well.

"The main thing to remember about water softening is that it has nothing to do with purifying, cleansing or conditioning the water," Robillard emphasizes. "It merely removes minerals that can be a nuisance."

Softened water is an advantage if homeowners experience soap film on pots, utensils and skin, or find that detergents are not cleaning up to expectations. "Softening technology can be designed to bypass toilets and outdoor fixtures that do not require soft water," Robillard says.

Water softening does raise the sodium level of water to about 7.5 to 8 milligrams per quart for every grain per gallon of minerals removed, which can be a health risk for people on low-sodium diets. "The final sodium level would be higher than 7.5 milligrams per quart after treatment," Robillard points out. "Depending on your water source, you may have to filter the water as well, before it enters the softener."

If consumers choose to soften water, Robillard recommends that the water be tested by an independent certified laboratory. "Water tests are not expensive and the results can help you resist buying softening equipment you may not need," he says.

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EDITORS: To contact Paul Robillard, please call 814-865-7158.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax