July, August and September of last year had an "official".64 of an inch of precipitation, where I live. Usually there is more but 1.5 inches is about what can be expected during those 3 months. Often the rainstorms are so minor that little water actually moves into the soil but simply evaporates, instead.
With large gardens on rocky soil, there is absolutely no way that I could grow most any vegetable without irrigation. My plan is to put about 1.5 inches of water on the garden each week. Any rain is mostly just ignored in that calculation since that's 3 month's precipitation in 1 week. It's a lot of water, about 1 gallon of water per square foot.
At one time, the water was not turned on for a lengthy time in one garden. It was my smaller garden but nearly 2,500 square feet. I considered showing up with the pickup bed filled with what water I could carry in 55 gallon barrels. That would be 45 barrels in 1 week at that garden! Move that much water by truck and by hand? It would be a monumental task!
Make everything as simple as possible but not simpler. ~ Albert Einstein