It's really simple...
Pull the plugs .. If one is water soaked It most likely a blown head gasket..
Fill it full of water and crank it..if it pumps water out the plug holes..it is a gasket / head or block..
Do a Compression/ leak down If it is blowing water as bad as you described you should have a Cylinder (or more) that has no compression..
Is it blowing water (tons of it) out the tailpipe..? Does it misfire? Does it blow White steam out the pipe? lock slightly on starting? all symptoms of gasket / mechanical damage.