If it's coming from the weep hole - the pump needs replaced.
If it's from the gasket - clean the engine side surface and water pump surface REALLY GOOD - green scotch brite pads, i'll even use very light grit sand paper on some, but you shouldn't do that unless you're very familiar with subaru/aluminum engine work like this. install a Subaru OEM gasket and make sure all the bolt holes and bolts are clean.
Buy a Subaru or AISIN water pump