How to test for the presence of water?

There are many ways to test the presence of water, usually we test it with anhydrous(無水，或脫水) solids with colored ions, such as copper(II) and cobalt(II).

For example,
water turns WHITE anhydrous copper(II) sulphate powder into BLUE.
It also turns BLUE anhydrous cobalt(II) chloride paper into PINK.

2006-11-17 16:52:58 補充：
Blue is the color of copper(II) ions.Pink is the color of cobalt(II) ions.

if water present

Dry cobalt (II) Chloride paper ----will changer color from blue to pink

anhydrous copper (II) sulphate --will change color from white to blue