Recently I've been playing football in the sun pretty hot temperatures. During the water breaks I tend to pour a lot of water over my head to cool me down, now this has an instant effect on cooling me down but in the long run would this have any affect on my body temperature? We know that the body cools itself by using heat to evaporate sweat on skin, would drenching my head and face in cool water affect this process or not?
Drenching your head and face with cool water will both directly cool your skin (because cool water is colder than you) and contribute to evaporative cooling. Your skin doesn't care if the water that evaporates comes from sweat you made, the pool, a water bottle or a hose.
The Khan Academy video is a good review of the principle.