My motor started pissing less and less on a trip out of town last year and it had me concerned. The guy at a marina suggested back flushing it with compressed air (blow air into the outlet hole with the engine shut down). It worked great. I have since replaced the water pump as it was overdue but I think salt/corrosion was the problem even though I religiously flush the thing after use in saltwater. I used a compressed air tank and it didn't take much. Don't put a hundred psi in there or who knows what you'll blow out.

My 2 cents