Why is there water draining into oil

Passages for water to migrate into engine oil are blown head gasket and cracked head, On engines that have coolant lines in the intake manifold, a leaking intake manifold gasket can allow coolant to enter oil as well. But I don't think that's in your engine. There are no oil passages at the water pump, so it's not likely anything you did. And you likely had this problem before, but you just didn't notice it.

A number of things it could be, blown head gasket, cracked cylinder head, cracked engine block.