Kevin Quincey, age 12, of Beaver Dam, Wis., for his question:

HOW DOES A WATER SOFTENER WORK?

We call it hard water when it contains lots of minerals. Hard water forms scale in pipes, boilers and other equipment, and it doesn't dissolve soap readily.

Lots of people solve the hard water problem by using water softeners. One type is called the ion exchange process. Water is filtered through minerals called zeolites. As water passes through the filter, the sodium ions in the zeolite are exchanged for the calcium and magnesium ions in water, and the water is softened. After household softeners become exhausted, a strong solution of salt is passed through the filter to replace the sodium that has been lost.

A lime soda process calls for the addition of soda ash and lime to water in a tank. Insoluble compounds settle to the bottom of the tank when the chemicals combine with.the water's calcium and magnesium ions.