200 HP Mercury

Went fishing last night (first time out this season) and water
pressure was only reading 10 psi.

That ended the great fishing expedition. I would not run the boat.

I picked up a new gauge today because the old one stuck some at lower
pressures. tested and still about 10 psi.

I also replaced the plugs because I thought I heard a slight miss last
PM.

What bothered me and heres the question. I had water on the plug in
#1 cylinder could this cause the loss of water pressure?? A cracked
head or cylinder?

I bought a new water impeller but wonder if I should install it.

Thanks for the input.

Richard