the way it is set up is...the tote on top has misters...i keep them running 24/7. that water drains into the rez in the bottom tote which also serves as a dwc tote for the rest of the roots. It has worked out so much better for me than soil has. I'm not sure the overwatering part. When i first looked into doing this i thought the same thing. while it has never been explained to me i'm just glad that it works... pics to come in the next post