I have done it numerous times without ill effects, I use mean green and a garden hose for big parts and mean green and sink for smaller stuff.
The trick is to let it dry
completely before you power up so it doesn't corrode your board or short anything, if you are worried about impurities then rinse with distilled water.
Really anything you do (or don't do) to clean electronics can be dangerous to them, the dust can create an insulator causing overheating chips, brushes can cause broken parts and scratched traces, water could corrode it and vacuums create static electricity, so pick your poison