To purify water that could be biologically contaminated, first strain visibly dirty water through a cloth. Use standard household chlorine bleach with 5.25% sodium hypochlorite as its only active ingredient, add 2 drops/qt (32 oz) or 1/2 teaspoon/5gal, double for cloudy water, stir, wait 30 minutes, a distinct taste or odor of chlorine should remain, if not, treat again and wait 15 minutes, repeat as necessary. The remaining taste or odor of chlorine is a sign of safety: if it is absent, the bleach may have lost effectiveness in storage (storage time is at least 2 years). Remember to loosen the cap of the water storage container and shake some treated water into the threads immediately after dosing to sanitize that area and prevent cross-contamination.