it depends on how much, but if the piston has filled, then its going to "hydraulic" and as mentioned abve, water doen not compress (much), so it could very well be new engine time!

remove the plugs, then try to turn over, if it still doesnt then remove the starter and try to turn it over remotely. also turn the engine over by hand, or atleast try, so that you cover most bases before spending money on anything.