The rule of thumb that I was taught for PP was
Add crystals to water until it is
Bright pink for drinking water
Dark pink as an antiseptic for wounds or a gargle for sore throats
Full on red for fungal treatment
Sprinkle crystals widely on snow as a dye marker
1/2 teaspoon of PP to 1 drop glycerine (or 1 teaspoon of antifreeze) for spontanious fire in a tight wrap of tinder
Ten to one mix PP and sugar for fire by grinding them together