Also worth noting, avoid getting soap or conditioner in the speaker. And, note that the Water Clear feature does not always clear the speaker completely, you may have to do it several times, lay the watch on its side, or you may have to let it dry out normally.
I've run into this myself several times where running Water Clear 4+ times, laying watch on side on absorbant cloth, etc do not clear the speaker. So far once it evaporates it's fine just sounds weird until then.
I believe the Apple info on this also mentions rinsing it in clear water and wiping down with a damp cloth in case you got soap or something into the two speaker slots.