My Subaru I have to put 3l of coolent every.

My Subaru I have to put 3l of coolent every morning and take the car for a spin to warm up then put another 2l in, after ive taken it for a short drive the water stop leaking, but when I stop (engine turned off) water starts to come out again. Ive been told its the water pump, but also my head gasget might be blowm. I don't want to spend the money on fixing the water pump if head gasget has gone, if there any way I could find out if head gasget gone b4 I replace the water pump?