Can water get into the manifold though the thru-hull exhaust?

[charlg]

I have the boat at the dealer for the coupler, and asked them to look into the rpm issue I have been having (port won't go over 3500 rpms). They did a compression check and found one cylinder low. When the opened the head, they noticed water in that cylinder only. The enging itself is fine. He believes is came down the center of the manifold and he's going to take the manifold apart and check the gaskets. But the manifolds are only 1.5 years old and the rpm issue was happening before they got changed. Is it possible that water is getting in there by way of the through hull exhaust, which I rarely use?