Bleach can be made as its needed if you buy pool shock with sodium hydro.....this is not the same as for purifyimg water. that is calciun hydro...
watch the percentage. i noticed pinch a penny is only 40 some percent. my local pool store is 73.
It recently came to my attention that Sodium hypochlorite is possibly the best option for point of use water purification.
Sodium hypochlorite is sold commercially as “ Dakin’s Solution “ or “ Eusol “.
Simple recipe, and the components last MUCH longer and are multi use compared to pool shock. Smaller storage footprint. Can be used for dental endodontic cleansing.
http://www.virginia.edu/uvaprint/HSC/pdf/09024.pdf
Directions on use for cisterns:
http://www.eastfremantle.wa.gov.au/uploaded/pdf/rain.pdf
General info:
http://en.wikipedia.org/wiki/Sodium_hypochlorite