Great question! We avoid soda cans like the plague when it comes to long-term water storage, and here’s why…
Soda cans are not made to last through the unpredictability of emergency situations. 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 thin. Dents from shipping or typical rough housing could weaken the liners and may cause aluminum to enter into your emergency water over decades.
The top of soda cans (where you drink from) isn't protected from the accumulation of dangerous toxins, chemicals, and particulates floating through the air during emergencies. And, to make things worse, the pop-top of the can is designed to go down into the can, which can push these contaminants into your water even faster. When you put your mouth to the top of the can and take a drink, the resulting possible diarrhea or vomiting can cause you to dehydrate faster than you can re-hydrate. A good pre-packaged emergency water, on the other hand, uses lids or something else to protect the drinking area where the mouth comes in contact with the container.
Another thing to consider is that the seams and pop tops of soda cans are weak points. Soda cans sometimes "pop" open over time simply from heat and cold shifts. Also, the CO2 or Nitrogen inside the can may even cause small holes in the seams of the can to expand over time because of all the pressure. It's not uncommon for soda cans to sometimes lose their pressure over just a few years of storage. You've probably seen that happen, right?