Little difficult to judge what exactly is leaking or more precisely, where it's coming from as when it indeed is leaking from the waterpump (thin O-ring gasket only), coolant may have spread working it's way out by pressure and deflected by wind whilst still rolling on the road.
What I would do is first pressurize the system by the use of special tooling, put on to the expansion tank instead of the cap. Then see if the pressure of ~1-1.2 bar will hold for approx. 15 min. If not, you have a leak. Either leaking outside, must be spotted somewhere, or you have a leak inside. Latter means the cylinder(s) are filling up (combustion chambers, so be aware of a possible water slot!) or it's leaking somewhere into the crankcase. Possible causes are leaking pipe (outside), blown head gasket or torn cylinder head (inside leakage).
If above procedure when cold is OK, then gently warm up the engine and repeat to see if the pressure is still being hold. If so, it can be that the propeller of the waterpump has detached itself from its axle. In other words is not pumping around while the pulley is being driven by your cambelt. In these cases the engine temperature very quickly rises.
If you are lucky and it isn't the head gasket, but just the waterpump, you must consider replacing the pump including a new cambelt + tensioner in 1 repair.
Hope it isn't all too bad (as in most cases)