How does water get pumped through an outboard engine?

The cooling water, at idle speed, is drawn into the water pump through the pickup screens, located on both sides of the gearcase. The water pump then forces the water out of it's housing, having been pressurized by the rotating rubber impeller, up through a length of tubing, into the powerhead. The cooling water now circulates throughout the powerhead, absorbing the heat generated by fuel combustion, and is expelled out through the exhaust.

At running speeds, the water pump acts as a circulating pump, similar to an automotive pump, as the water is forced into the pickup screens. At higher speed the pickup screens act like scuppers, picking up the water and forcing it into the pump. 

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