Eh?You went to wash the car, and just by chance - the cylinder head happened to blow, when the car was off and stationary?
got up today and thought i would do a few checks on the golf and give her a wash. so i popped the bonnet to find my cylinder head pissing out water. so it looks like a new cylinder head gasket and a rebuild.
No reason you can't start the engine after you've done the oil/water/fluids checks as the last thing.