During an emergency, if the safety of a drinking water supply is questionable protect your health:
Disinfecting with bleach may be more practical than boiling especially when large volumes of treated water are needed and there is no means available for boiling.
Measurement guide for treating water
Before using, let the mixture stand for 30 minutes to allow the chlorine time to kill any harmful organisms.
For more information: http://www.nemo.gov.lc/Disasters.aspx