Nobody directly draws water from Lake Powell. It serves as a buffer to keep the Colorado River Compact operating normally.

Upper Basin States (Utah, Colorado, Wyoming and New Mexico) are obligated to deliver 7.5 million acre-feet of water to lower basin states (California, Arizona and Nevada) annually. Lake Powell captures excess water so we can make these deliveries in times of drought without dipping into local supplies. When it’s gone, lower basin states can technically call on upper basin states to send down their water, which would drain local supplies.

So in essence, everybody relies on Powell. Including Salt Lake and Utah Counties.