Since you are concerned about Crypto, you don't want to use chlorine since that will take too long to inactivate it. I suggest you take a look at Katadyn Micropur MP1 Purification Tablets that are a combination of sodium chlorite and Dichlor that when dissolved in water will generate chlorine dioxide that will kill Crypto though it takes 30 minutes in clear water and 4 hours in cold and extremely dirty water. Everything but Crypto is killed within 15 minutes.