I recently attended a class on water storage and things to consider. It was a great reminder of many of the things I have learned in the past, and I also learned something quite important. Household bleach has a shelf life! Many of us at the class had not heard that bleach will break down and lose its potency beginning at about 6 months. If your bleach is older than 6 months you will have to add more bleach to your water storage to be sure it kills all the unwanted germs. It is recommended that you replace your bleach every year so you can trust its potency level.
I've included a link to an article from clorox that supports this information.
For more information on water storage click here.