Nearly a century ago in some part of the valley the Salt River Project distributed water by a network of canals to framers.  The bulk of this farmland is now residential.  The canals remain, some 132 miles of them which are maintained by SRP up to a certain point then taken over by neighbhorhoods, the lateral canals.  These distribute water from the mainline canals to individual homes.

From the SRP website

"SRP brings water from the high country to the desert below through a complex system of dams, lakes, canals, laterals, ditches, pipes and valves.

Most of your water originates as rain or snow in the mountains. The SRP watershed is a 13,000-square-mile area draining into the Salt and Verde rivers. The watershed extends from the White Mountains near the New Mexico border to the Seligman area in north central Arizona.

The runoff from the watershed is collected in six reservoirs: four on the Salt River and two on the Verde River.

SRP's system also includes about 250 groundwater deep-wells throughout the Valley that help us meet shareholders' needs.

So how does the water get from the reservoirs to your yard? SRP uses the most cost-effective, efficient water transmission method available: gravity. Canal water is moved almost entirely by Mother Nature.

After you place your water order, we combine it with all the other water orders from the Valley, and release the requested amount of water from the storage dam. The water then flows into the seven main canals crossing the Valley.

An SRP employee known as a "zanjero" (pronounced sahn-hair'-oh) opens a gate to release the water from the canal into a system of smaller waterways called laterals. The lateral brings the water to a specific delivery point where a zanjero opens SRP's gate, releasing the water into your neighborhood.

The neighborhood delivery point is the end of the SRP system. From here, the system bringing water to your property is made up of open ditches, underground pipelines, control gates and valves. This system is owned, operated and maintained by the people who use the system in your neighborhood and is referred to as the "private system."

You and your neighbors are responsible for seeing that the water gets from the SRP delivery point to your property. To do this, make sure all gates and controls are set properly and keep the system in good repair."

There are about 23,000 residential customers  who have irrigated lots, mostly in older established neighborhood like North central Phoenix.  Irrigation is a great way to water deep.  When lots are irrigated they often don't need supplemental watering like sprinklers. 

Although we do have sprinklers in some of our properties, they are never used because irrigation is sufficient to keep the grass green and healthy, as well as the trees and other plants.
Read more about irrigation here