I don’t think anyone would argue that access to water is one of the most important factors that determine what you can grow and whether you can make a living farming. Here in the Southeast, we get on average 50 inches of precipitation, mostly rain, each year, with moisture streaming in from the Gulf of Mexico and the Atlantic Ocean as well as carried overland from other parts of the United States, including many irrigated areas in the central part of the country. That gives the Southeast more resiliency to drought than many other parts of the United States, even though high temperatures also increase evaporation from lakes and streams and evapotranspiration from plants. In the Southwest, by comparison, the water supply is much more limited, and farmers there depend on historical water laws to get access to irrigation water for their crops since precipitation is lower. Here is an interesting story from ProPublica that describes how a small group of farmers in the Imperial Valley gets a large portion of the available water from the Colorado River due to their lengthy history in the region when water rights were just being developed.
