Had water in my engine and now it is knocking what do you do?

If you suspect water has entered your engine and it's now knocking, stop driving immediately to prevent further damage. Remove the spark plugs to check for water in the cylinders and drain the oil to inspect for contamination. After addressing the water issue, replace the oil and filter, and consider having a professional inspect the engine for any potential damage. Avoid starting the engine until the source of the water is resolved and the engine is properly serviced.