When you go swimming, you submerge your body in water. If your head is out of the water, it is not submerged — it's just wet.
To really soak a washcloth, you should submerge it in a basin of water. It is said that the word submerge was invented by William Shakespeare. We don't know that for sure, but we know that its appearance in the play Antony and Cleopatra is the first recorded time the word was written, and therefore read, by anyone.