Firstly, where is it leaking from? If its from the gasket seals around the water pump body, you can use rtv sealant to re-seal the water pump.
However, if it leaks from the pulley bearing, I'm afraid you will have to change the entire pump.
It would appear that the Christmas holidays don’t do much to slow things down at Subaru’s performance division, STI. On the very same day that they unveiled the WRX...