Magic Sand is regular sand which has been dyed and coated with a hydrophobic substance -- a substance which repels water.
Oil, for example, is a hydrophobic substance. Pour a little oil into a cup of water and the oil does not mix; it simply floats to the surface. Magic Sand works just the same way except that Magic Sand sinks. The coating on the outside of the magic sand repels water and keeps the sand dry!
To store, simply remove the sand from the water with a spoon... it is perfectly dry! Comes in one pound packages.