Potassium permanganate - This is another cheap and easy way to purify water. Potassium permanganate crystals can be bought from any chemist and you need add only about 3 or 4 crystals per litre of water (or until the water stains a light pink) and leave for 30 minutes. Potassium permanganate can also be used as a disinfectant for cleaning wounds, add crystals one by one until water turns purple (approx. 0.01% solution). 

As an oxidant, potassium permanganate can act as a disinfectant. For example, dilute solutions are used to treat canker sores(ulcers), disinfectant for the hands and treatment for mild pompholyx, dermatitis,^[4][5] and fungal infections of the hands or feet.^[6]Potassium permanganate, obtainable at pool supply stores, is used in rural areas to remove iron and hydrogen sulfide (rotten egg smell) from well and waste water. Historically it was used to disinfect drinking water.