Bea Harbin, age 13, of Twin Fails, Idaho, for her question:

HOW DO YOU MAKE SOFT WATER?

Water softening is a method of removing from the water most of the minerals that make it hard. Hard water does not dissolve soap readily. The principal methods of softening water are the lime soda process and the ion exchange process.

In the lime soda process, soda ash and lime are added to the water in amounts determined by chemical tests. that settle to the bottom of the water tank.

In the ion exchange process, the water filters through minerals called zeolites. As the water passes through the filter, the sodium ions in the zeolite are exchanged for the calcium and magnesium ions in the water, and the water is softened.

After household softeners using the ion exchange process become exhausted, a strong solution of sodium chloride or salt is passed through the filter to replace the sodium that has been lost. The use of two exchange materials makes it possible to remove both metal and acid ions from water.