These are parts lubricated and sealed at the factory and unable to be serviced. This sealed or non-serviceable part does not mean that it is air tight. Therefore, even on a cooled unit, sprayed water can get into these components, carrying in dirt, debris and other contaminants while rinsing away necessary lubrication. Again, this causes the risk of internal rusting resulting in accelerated wear and premature failure. To properly clean your unit, you must first wait for it to cool.
Some consumers own air compressors.
If you do, you can use air to blow dust and debris off of the unit. If you do not, cleaning methods should consist of using a brush or broom to clean away any and all debris from the unit. Make sure to clear debris from the muffler area along with all engine and on units with transmissions, the transmission cooling fins. Use a damp cloth on components that get hot during operation to ensure they are cleaned of any caked on debris. Examples of these components would be the engine, transaxle or transmission, and the chain case on tillers.