Correct me if i'm wrong but if it was the water pump i don't think this would explain your extreme water loss unless your head gasket went with the car overheating and also your temp gauge would rise especially if you engine was hot enough to boil the oil. I think your best bet is to put it into a garage and get it diagnosed by a professional. You could end up splashing out 250-350 to get the pump done then to find out the pump was fine.