I use the ratio of 8 Drops of Regular Bleach (non-scented and non-additive) to 1 Gallon of water, or 2 Drops of Bleach per Quart or per Liter on my stored water. Other than tasting flat, I had a couple gallons of water that I failed to change out for about 4 years that were fine. I also have a Katadyn Pocket filter with a Carbon Cartridge and a Sawyer SP 135 I could use as backup to filter the water if I feel it was stored too long.

The only problem I've had with stored water thus far is with some rats that got into my storage area a couple of years ago. I lost about a half a case of store bought bottled water (and some dried pasta). They would chew through the top of the PET bottles, drink as much as they could reach and then would chew through another bottle. All of the water was stored off the ground on wire shelving, but I failed to notice that a cooler I had lent to a friend was put back next to the shelf in such a way that the rats could run up the cooler's handles and get to the water.

I've thought about using some of the colloidal silver solutions on some of the stored water after reading a paper on hospital sterilization plans, but never followed through due to potential risks with long term intake.