Water in the oil?

Hello,

Do you mean coolant in the oil? Typically coolant will mix with engine oil if the head gasket is blown.
When that happens you will get a lot of white smoke out of the tail pipe and your oil will be milky color.

https://www.2carpros.com/articles/white-smoke-or-steam-coming-from-the-exhaust-pipe

You can also test for the blown head gasket. It checks for combustion gases in the coolant.

https://www.2carpros.com/articles/head-gasket-blown-test

In order to fix this issue the head gasket have to be replaced.
Which will require you to remove the intake and exhaust manifolds along with the cylinder head of course.

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.