Make sure the water storage container you plan to use is of food grade quality, such as 2-liter soda bottles, with tight-fitting screw-cap lids. Milk containers are not recommended because they do not seal well.
If your local water is treated commercially by a water treatment utility, you do not have to treat the water before storing it. Treating commercially-treated water with bleach is superfluous and not necessary. Doing so does not increase storage life. It is important to change and replace stored water every six months or more frequently.
If your local water is not treated commercially by a water treatment facility, that is, if your water comes from a public well or other public, non-treated system, follow instructions about water storage provided by your public health agency or water provider. They may recommend treating it with a small amount of liquid household bleach. Still, it is important to change and replace stored water every six months or more frequently.
If your local water comes from a private well or other private source, consult with your local public health agency about recommendations regarding storage of water. Some water sources have contaminants (minerals or parasites) that can not be neutralized by treatment with liquid household chlorine bleach. Only your local public health agency should make recommendations about whether your local water can be safely stored, for how long, and how to treat it.
If you plan to use commercially prepared "spring" or "drinking" water, keep the water in its original sealed container. Change and replace the water at least once a year. Once opened, use it and do not store it further.