Irises love water, you can water them all you want here in the Phoenix area.
I planted an iris bulb here in Glendale, Arizona (a suburb of Phoenix) on October 10th. The leaves started showing about three weeks later, and now on November 29th, it's growing strong. It will flower in February, and will grow much taller by then.
Irises love it here, and they do great. And they LOVE water. In fact, the only time I've ever had problems with them is when they have dried out (the air is very dry here in the desert). They did their best one season many years ago when I forgot to turn off the automatic watering system in the winter. So water them all you want.
I fill a watering can with Miracle-Gro and water them whenever the mood strikes me, which is often, sometimes a couple of times a day. No, they won't die if you miss a day, but you don't have to worry about over-watering them. My point here is that if you're one of those people who always fed their goldfish too much, or can't stop giving treats to your dog, go ahead and be generous with the water on your irises. You won't kill your irises with a lot of water, and they won't get fat. They'll love it.
Since I will be turning off the automatic watering system for the winter in a couple of weeks, I will continue to hand-water my irises. I have two of them recently planted in my backyard, and as usual I have done just about everything I could think of - they're planted in an area that will allow them plenty of room, along the path where I can reach them easily, in potting soil with moisture crystals and slow-release fertilizer. Yeah, I'm a little crazy. I even bought the bulbs from a mail-order company, which is more expensive than getting them at Home Depot, or the Dollar Store. But when they bloom, they will be awesome.
If you missed my blog post on how to plant an iris, it's here> http://bradstropicalparadise.blogspot.com/2016/10/how-to-plant-iris-in-phoenix-arizona.html
|What my iris will look like in February. Photo from Easy to Grow Bulbs|