Water storage

I have three, 7 gallon jugs of water. The jugs were from the camping section at walmart.  I can’t remember how old that water is, but I wouldn't want to drink it. It’s at least five years old. Can I just dump it and refill or do I need to clean or sanitize? I’m thinking it would be best to put a little bleach in for a day or two then rinse? How much bleach?

I am sure I have drunk worse than what in in there.  Out of an abundance of caution,  I would clean them out with one cup of bleach for each gallon of water.  Rinse. Refill with 10 to 12 drops of bleach per gallon of water.

I would  not add more bleach after that.