"Moisture eater" is what they called the machine that the Great Heep put on Biitu.
The Heep, which was put in place by the Galactic Empire to manage the planet's mining activities, utilized the moisture eater to gather water from the nearby farms. This water was then used to keep the droid's massive internal systems from overheating.
This caused a drought that devastated the Biituian farmlands in the area, and it was this unfairness that motivated the explorer Mungo Baobab to take action. Mungo, along with his droids (R2-D2 and C-3PO), managed to disable both the Great Heep and the moisture eater.