it could be numerous things.
why dont you take a flashlight, hang out for awhile when the engine open, and see where its leaking from. it took me 1 month to diagnose my coolant leak...what i can recommend is buy an "additive" for your coolant, like NEO SYNTHETICS additive, it goes in there, but when it dries*after leaking out* it turns white so you can see where it is all comming from, and yes, mine was the water pump.