Your bearings will have seals on them... when the seal fails to the point that water gets in from clean up... there will be a lot of dirt and other things getting int it...
A good flushing with water is going to keep things clean.
I would not necessarily want to submerge the thing or use a power washer directly at the seals...
On your rider if the mower spindles are grease able, a shot of grease will push out any water, If they are not grease able then they are sealed, and this will not be an issue... :smile:KennyV