They do.If watering cans work on cacti, though...
I liked the cacti because, once I finally got enough of them to plant in a spaced 8x8 pattern (the can REALLY helps here, and you don't need quite that many), I no longer needed to cook bottles to drink and could use the dirt for other things. They grow on their own fast enough that I got more than enough for two days of water when harvesting every two days.