Kostas

I am with Tommy on watering and believe deep watering them less often is best as it makes them establish a better root system and minimizes the risk of rot. They also dont seem to be affected by drought as much once established,even if the irrigation fails for some reason. In my Pyrgos garden,i water them every 5 days now and we are in the 30's C. Of course humidity is high and ground water level is high as well,which helps a great deal as the bananas can get self sufficient once established in my case as i guess in Tommy's case as well.
Of course,i dont have experience with a desert environment but my palm loving friends from AZ have had the best success using deep watering on their palms once a week and their palms grew perfectly. So,i would guess twice a week at most would satisfy the bananas if deep watering(slow watering via drip emitters for a long period of time). The adjustment needs to be gradual though if you want them remain in excellent condition as the current root system is most probably shallow and wont be able to use the water available deeper until it expands following some drought stress.