Cactus in pots require more care in watering than in the ground. In the growing period which can be spring & summer or fall & winter. Depending on where they come from, south America or north America, the plant should not be allowed to go completely dry, just moist. In the house watering could be as little as once a month depending on the dryness of the house. But outside as much as every two or three days. Take a wooden pencil or dow rod and place it down through the soil to the bottom of the pot, when removed, if damp soil is on it don’t water. After a few try’s you will learn when to water.