I contacted Federal Premium, Winchester, and Remington, as well as a small bulk ammo re-manufacturer near me about this. I don't have the emails anymore, so I'll just give you a quick rundown (all four companies said basically the same thing).
As somebody said already, modern ammo is sealed very well. As for dunking it in water, that's not a problem. The problem comes with temperature differences, causing the metals to expand and contract. Basically, if stored in a cool, dry(ish) place (really anyplace inside), the ammo will last AT LEAST 10-15 years, and function without issue. After that, there may be a small number of failures, like a couple every thousand. So, as for shelf life, don't worry about it.
For carrying in a gun, the life expectancy is much less. This is especially true if you carry in a humid climate or with a heavily oiled gun. All companies recommended target ammo to be used/replaced after at least a year. Both Federal Premium and Winchester stated that the high-end self defense ammo is made with much closer tolerances. (Federal particularly addressed my carry ammo, Tactical Law Enforcement HST.) This high-end self defense ammo is good to carry every day in a pistol for up to 3 years. This time-frame includes extreme climates, such as Alaska were the firearm and ammo could be subjected to a lot of moisture and temperature differences of over well over 100 degrees.
Basically, don't worry about it. I don't know about you, but I shoot every week, and my SD ammo gets a workout at least once a month, so It's not really an issue. And honestly, IMO, if your not shooting your carry gun for 1-3 years to keep up your skills, then you have no business carrying a firearm.