I buy 4-packs of 2-litre bottles from a supermarket. They have an expiration date of a year or two and I am happy to keep them a few months beyond that. I also buy smaller bottles which I find convenient for camping and they mostly get used with a year.

I also have a fish aquarium with about 160 litres in it which gets changed to suit the fish. It gets refilled from a 40-litre tank and you have to tap water to stand for a day before giving it to the fish, so I try to keep it full all the time.

I don't bother with storing tap water otherwise, because I don't think it's worth the uncertainty about expiration nor the effort of replacing it frequently enough to be safe.