Water Cooler Fans?

This question might seem dumb, but why do water cooling radiators need fans? 

To keep the radiator/ water cool (just the same as looking that the radiator in a car)

Oh ok, but how does having the physical radiator help with that, wouldnt a metal plate thats touches the water be better?

Thats what a radiator is only bettter, instead of one plate a rad is corrugated and passes liquid around meny smaller pieces of  metal that are cooled helping dissipate heat

Its has to do with Surface area and the Volume of Air able to pass over said surface area dissapating the heat in the liquid being fed through the rad.

you need that air movement to help take away the heat