You can splash water on an air filter all day long, it wont do any damage. An engine will ingest water as a spray safely until it dies from extinquished combustion. The damage occures when water is sucked in volumes large enough to stop the pistons upstroke due to hydraulic lock. Since fluid does not compress like gas, it has no where to go and stops the piston, damaging the piston, rod or whatever gives out first. Just getting the filter wet from rain or splash will not do this. Hell, a spray of water called "water injection" is sometimes used to cool the combustion temps in turbos. So just getting the filter wet will not harm the engine at all. Bottom line is ... you have to submerge the intake in water to damage the engine.