The majority of the work would likely be maintenance on the vaporators and other equipment (such as droids). Tattooine is a desert world. That means sand. Sand gets into all sorts of gaps and crevasses, which will interfere with the working of the equipment. If the vaporators aren't working at full efficiency (or at least close), they won't pull as much water out of the air, meaning a smaller harvest or maybe even no harvest at all.
They would also have to monitor the vaporators to ensure that no one else (other farmers, scoundrels, or sand-people) raids the vaprorators' storage containers.
The assumption that a moisture farm would involve little work, because you just have to haul the water into town, is like assuming that a modern farm involves just a little work because you just have to plant and then haul the crop into town. While planting season and harvest season are the two busiest times of year for farmers, they don't exactly sit idle for the rest of the year.