Lake Mead's white bathtub ring marks how far the reservoir has fallen upstream of Hoover Dam. Mead and Powell's combined storage is the lowest since 1957.
The two Colorado River reservoirs that supply water and power to 40 million people keep dropping in a 25-year megadrought, while the seven basin states remain divided over long-term cuts.
The Board of Water Commissioners voted Aug. 26 to end the lawn watering season Oct. 1 for the utility's 1.5 million customers. Spray irrigation is out, trees and gardens can still be hand watered, and violations carry escalating fines up to $1,000.
Forecasters say a tropical moisture-fueled system will bring heavy rain Wednesday, with flash flooding the main threat and mountain snow chances below 30 percent.
Federal officials released the final environmental review July 31 and operating guidelines Aug. 21, setting an adaptive framework for the river through 2036.
