Do NOT wash the engine with water as it's usually not a good idea. If you do want to clean any parts of it, like spilled oil, be sure that you don't get water under the top cover where the spark plugs are (brakeclean is better for oil spills).

Often, our used car dept has the engines detailed and after hosing the top of the engine, the spark plug holes fill with water, it misses and sets misfire codes (check engine light), then the plugs foul and the oil gets gassed.