Not to be confused with the blue flowered annual of this genus (Lobelia erinus), Lobelia laxiflora has been on my list of dependable water-wise perennials for quite a while. It is native to Arizona and Mexico. Commonly it is called Mexican Lobelia. This perennial is one tough cookie.
As far as availability is concerned, it is not a front-row-center type, but it can be found fairly dependably at nurseries in my area (Corona-Riverside, CA). I imagine most people growing water-wise perennials will know this one.
Lobelia laxiflora will tolerate regular irrigation or dry conditions – 10 points in my book. The plant has a floppsy sprawling habit, open and lose. Its appearance is soft, due to the many narrow green leaves that cover the plant; another valuable asset for a low water garden – green foliage. It grows in sun or light shade. It gets 18 to 24 inches tall and about 3 feet wide; actually it spreads over time by underground rhizomes. I have not found it to be invasive, perhaps because it won’t run with a limited amount of water. That’s the thing about water-wise practice; it slows everything down a bit, which is good. We could all use some slowing down now and then. Then we will notice the birds eating fluff out of a dandelion. Or drinking nectar from brightly colored tubular flowers which are perfectly engineered to provide attraction and sustenance and leave room for the hover-fly wings of a hummingbird, I love that about plants and birds. The way they work together.
In my experience this is an easy plant to grow in Sunset zone 19 where I live, (USDA zone 9b). If you don’t see it in your nursery, ask for it.