what is the difference between coin battery and alkaline battery
"Coin" is a physical "form factor" or shape of a battery cell. The more common form factor is a cylinder (like a AA cell, etc.) 
Alkaline is a type of CHEMISTRY of the battery cell. Different chemistries of batteries can be found in various form-factors. There is no particular correlation between the form-factor and the chemistry of a battery cell.


Whether a particular battery cell can survive under water has nothing to do with its form-factor or its chemistry.  Most batteries are not designed to operate submerged under water. No matter what size, shape, or chemistry they are.