I have 30 gallons of Ozarka water and they are made to stack on top of each other so they only take the space of 10 of them. I have a 55 gallon water barrel attached to a diverter in one of my down gutters. I have two children's plastic pools to blow up and catch rain water on one of my outside decks. We tend to have plenty of rain water all year, so those are a renewable source of water. Our small group of houses have a 15,000 gallon pool right across from my house in here. I have a WaterBob, food grade plastic, for my bathtub, that holds 100 gallons of good water from the faucet.
I have a Big Berkey water purifier that can turn water in a ditch to pure water. Any water I collect from the outside, like the water barrel, goes through the Berkey so I know it is pure. A purifier is different than a filter, such as those pitcher filters. They will not get rid of tiny bacteria, etc. The Big Berkey takes out all that so you have pure water. A Berkey is expensive, $200+ depending on the one you get, but you are assured of pure water.
If you don't have a Berkey, you need to find the description on the net and get one.
I have four Katadyn siphon water purifiers, too, that I got years ago before the Berkey came out. It is a purifier, not just a filter. I think those were over $100 back then.
First of all, milk jugs do not degrade quickly. Unless you call over a year or two, quickly. They will degrade over time but that is absolutely zero problem. I replace them far sooner than they go bad. I have yet to find a bad one among my stored ones, tho I have come across very old plastic bottles in the woods which were cracked. If I left them out in the sun then yes sunlight would destroy them.
I live in Northern Florida and have had no problem with them freezing and I store them outdoors tho in a covered area.
I guess I am a bit lucky in that I don’t really have to store water at all as I am near spring water. I keep it for convenience in case the power goes off for a while and that is about it.