Barb Sass, age 10 of St. Paul, Minnesota, for her question:

What causes hard water?

Pure fresh rain is called soft water. It works with soap to form lots of foamy bubbles and get out the dirt. But water is a chemical that tries to dissolve all sorts of other chemicals. When it dissolves chalky, calcium type chemicals, it becomes hard water. And hard water refuses to work with soap as it should. Instead of frothy foam, it forms dirty scum that leaves a nasty ring around the bathtub.

Our water supplies come from rain. But before we get this water, it gathers in lakes and streams or sinks down to collect underground. And all the while, the gathering water tries to dissolve chemicals from the ground. When it seeps through limestone, it dissolves the calcium type chemicals that turn soft water into hard water. Then we have to add water softening chemicals. They sift out the hard chemicals so that the water can form soapy bubbles and get out the dirt.