Yes, water is perfectly safe to spray on your engine. Engines are designed to handle rain and puddles which means spraying it with a hose is safe. However, using a pressure washer would be overkill and could damage some of the more fragile parts in your engine bay. It’s a good idea to let your engine dry thoroughly before driving your car again. Leave your car outside (preferably not while it’s raining) with the hood open so it can dry out.