It's easy to forget how important water is in our lives. Of course we need it in our diet, but in our homes, it's a tool--a fluid medium that carries material from one place to the next. And one of the reasons it does this job well is that it's very good at holding things, either by suspending them or dissolving them. Unlike most tools, though, water doesn't come with an instruction manual.

If it did, you'd know why the dishes you thought were washed are covered with spots when dry, why the water in your shower leaves a film on everything it touches, and why what you thought was clean water has clogged up your plumbing system.