Cacti & Succulents cover just about all plant genus, so they are not a group of plants, they have all just adapted to life in a harsh, dry environment. In this respect they are all drought tolerant.
Although many of these plants can survive with no rainfall, they do need water to grow. Grown in the open ground they tend to have spreading root systems that capture all moisture over a large area. In many desert areas they will rely on the dew that forms as temperatures fall ovenight. In pots they are denied the widespread root area, so will need some form of watering during the growing season.
With Cacti & Succulents the most important thing is the soil. It needs to be free draining. Many of the watering problems you hear about are as a result of stodgy multipurpose compost used by nurseries. This makes watering an art.
With adequate drainage you should be able to water every few days in the growing season, and every day in hot weather, with no danger of rotting the roots.
We need to distinguish, at this point, between the Desert Cacti, and Succulents.
Cacti should be kept dry outside the growing season, which here, is October to April. Succulents on the other hand, need a small amount of moisture to maintain them in good condition. With perfect drainage, watering sparingly on a sunny day, just to moisten the top of the soil should not cause rotting of the roots.
These plants survive, in a desert, but need some water to grow well.