Generally, you should not need to add water to the hungry bin. Food scraps have a high water content, which helps keep the bin moist. The design lets excess water drain from the bin but ensures enough moisture is retained to maintain optimal conditions. The worms do need to be moist, though, so if the bin has dried out, sprinkle a little water on the top of the bin. If you have added dry matter like shredded paper, you may also need to add water. Take care not to drown the worms; the top should only be as wet as a wrung-out sponge.