You have water in your engine from a blown head gasket what do you do?

Obviously you will have to replace the headgasket. Depending on the engine type and configuration, it may be a major process. Once the head has been removed you should take it to a machine shop to have it "planed", meaning that if the head gasket blew the head is probably warped and you have to do something to make it flat again. It can be out just a couple thousandths of an inch, something that you couldn't even detect, and that would be enough to cause the head gasket to leak. If you don't have experience with this, take it to a reputable mechanic.