If you can't find the exact numbers, it's okay. NO cacti or succulent grows in an absolute desert. They have evolved to hold the water from the wet seasons until the long dry season is over. They do not hold water because they want to, but because it is necessary for survival in their native habitat. A plant in a pot is NOT in its native habitat and should not be treated as if it were.
More succulent plants die from lack of water than any other reason.
Water at regular weekly intervals. Lightly when the plant is dormant, and thoroughly when it is in full growth. When a pot of soil becomes very dry, the roots also dry out and begin to die. If the plant is watered after the soil dries, bacteria and fungi attack the weak roots and enter the plant. Most cacti do not grow out in the full sun until they are large and mature.