Every May I buy 12 1-gal jugs of water as part of our preps. If a hurricane is coming I also fill up to six 7-gal Aquatainers and several 3-gal aquatainers. The aqutainers get dumped once the "all clear" sign is given. The 1-gal jugs get replaced yearly unless I use one before then. The used one gets replaced the next time we are at the store.
-Blast
I like to keep a minimum of 20 gal in my supplies, and currently have 24. As I use 1 or 2 gal up, I'll replace them with fresh 1 gal water bottles from the store.
I have about 60 gal in empty aquatainers and 5 gal industrial water coolers that I can fill up fast if needed, plus 60 gal in my hot water heater.
My water filters can filter several hundred gallons if needed. The supplies I keep in Houston have a reverse osmosis hand pump that is slow, but with work can do several gal of fresh from salt water daily if needed. My stored water in Houston needs to be replaced as I like to do it yearly but haven't been there in 1.5 years to do it.