Brian Price, age 9, of Sioux City, Iowa, for his question:

WHY IS THE RAIN SOFT WATER?

We notice the difference between hard and soft water when we take a tub bath. The soft water works with the soap to froth up a lather of foamy bubbles. That lovely white lather gets the dirt off your skin, and when the soft soapy water drains away it leaves the tub nice and clean. Hard water turns the soap to nasty scum, and it leaves a grimy ring around the tub. It is hard because it seeped through the ground and dissolved a lot of limy chemicals.

Ground water is softer when it does not seep through limestone rocks. But the softest soft water falls down as raindrops from the clouds. The misty droplets in a cloud are pure water. This moisture dried up from the sea and left all the hard chemicals behind. Some rainwater gathers a few impurities as it falls through polluted air. But most rainwater is very soft and eager to make soapy foam  because it has no dissolved chemicals.