To purify water for drinking, you want it "just" coloured. As an antiseptic wash for wounds etc, a light pink; as an antifungal for athletes foot (tinea), crotch rot or ringworm, a full red saturated solution. The solution is a strong oxidiser, and can actually do harm to living tissue in a wound, so use sparingly. It will stain skin and clothes brown.

The solution works best on pre-filtered water - get rid of as much suspended clay and organic material as possible - even strained through a folded handkerchief or shirt.

Take a clear tumbler of water. Add one or two crystals. Mix well.

A little goes a long way. A few crystals ( a match-head worth?) would treat a full litre of filtered water.