Great question! We avoid soda cans like the plague when it comes to long-term water storage, and here’s why…
Soda cans are made to last about a year or so, not decades. Soda manufactures have spent years at finding and developing the thinnest, cheapest way of putting their drinks into a can, so they can maximize profit - that is the aluminum soda can! If these manufacturers were concerned about longevity, they would still be canning in pure tin cans like they used to during World War II or in thick HDPE plastic like we do, but that gets way too expensive and would cut into their profits.
Also, the liners inside aluminum pop cans are so thin that all it takes are little dents or some rough housing (something as simple as just shipping a product to your doorstep), and your water could get contaminated by soaking in the aluminum. That’s a very bad thing.
Soda cans also can collect bacteria and contaminants on the lids of the can over time or during a crisis, which can get you sick when you drink from it. The pop-tap of the can is also designed to go down into the can, which can push those contaminants into your water even faster. During emergencies, for example, chemicals and particulates float through the air or are able to soak the cans. Those types of contaminants can cause sicknesses that can defeat the whole intent of drinking the water in the first place (including diarrhea or vomiting, which can dehydrate a person faster than that person can re-hydrate). A good pre-packaged emergency water protects the drinking area where the mouth comes in contact with the container. Soda cans are not built with that type of protection.
Another thing to consider is that the seams and pop tops of soda cans are weak points. Soda cans sometimes pop open over time from heat and cold shifts in the air and the CO2 or Nitrogen in the can even cause water vapor to escape through the micro holes in the seams of the can. For example, go on Ebay.com and look for 20-30 year old soda cans. Most of the sellers talk about how their cans were NEVER opened, but all the liquid somehow is gone out of the can. Case in point!!