Really cool! This device mounts in the pond and refills to the set line whenever the water level drops! Very cool invention - this durable little device mounts in the pond and is fed by a ONE INCH line. Most units are fed by the average icemaker line and honestly couldn't top off a summertime pond if it had all day. This unit comes on when the water level drops below the set point and shuts off as soon as it senses "full" Reliable and useful! Care should be taken in winter as the line could freeze, preventing the unit from being able to fill the pond. This is a must have for busy koi keepers!