Common sense, cacti can do well on their own without much tenderness. In summer time, you can water it once a month, while no additive water in winter time. Nowadays, gardeners culture this plant into good looking and good shape, so they are really beautiful houseplants. Another case is water plants, such as water bamboo or water lily. Since they live in water, you don't need to watch on them to see if they need more water, but just change sometime.