It should last longer if kept cool. And actually since its been canned its sterile too
You might have to pour it back and forth into another jar to aerate it a little for the taste after you open it
Pure water can last forever if canned without the use of any metal. Water is one of the best natural solvents and will hold a large amount of metals and salts.
Pure water (H2O) won't absorb radiation directly but the elements dissolved within it will. It won't spoil but will dissolve poisons and toxic elements. UV radiation can break the molecular bonds over time but they naturally return to their previous state.
No matter how well you filter and purify water it will always contain some amount of "contaminants". For instance, if you use an aluminum canner the water will contain traces of aluminum and if you use a stainless steel canner then you will have traces of iron and chromium and possibly molybdenum.
These contaminants are at such levels that they can't hurt you under normal conditions but it does give someplace for radiation to attach and make the water toxic. The radiation can come from cosmic sources, natural radiation from the ground or a nuclear event. The only really dangerous source would be a nuclear event and at that point all canned goods would be suspect if they were exposed to the direct radiation or directly contaminated with fallout. Under those conditions the canned food would be the least of your problems.
I don't know for sure, but I would think that canning water in a canner would give it a long shelf life. I think anytime we have empty canning jars, and are canning something, that putting jars of water in the canner is a wise thing to do. I really believe that many of us will not have enough water stored in a SHTF situation. Those who have wells will be in a great place, as long as the well doesn't go dry or get contaminated.