waterleak when engine is warm

From what part of the engine compartment are you noticing the leak? Cooling systems in an automobile are pressurized from 13-15 psi when the engine is running, so often a coolant leak can come when the engine is hot, but not be as visible when it is cold. A pinhole leak in a hose, a leaking head gasket, a leaking radiator, leaky water pump, etc., could all be the problem. Need more information to fully answer this.