I just hardly ever water mine, I just allowed it to crawl up a wall, onto a chain link fence. ( about 20 feet in the air ) at one time the main feeder from the ground broke, but it manages to stay alive and produce fruit with its roots and sent down some more ( i think ) I have already gotten about 8 Pitayas from that plant this year, and has 3 more still on it.
Although they are cactus, and can really stay alive in long droughts, they do thrive on some moisture. , we have had regular rains this year, and no dry season, so they do well, I do not spray them with anything, and they keep growing like weeds here.