The story of L.A.’s water supply in the early 20th century isn’t pretty. The monuments of the Los Angeles Department of Water & Power are another matter. The electricity-generating substations of the ’20s and ’30s are art deco and Greco-Roman temples to the public good. With its eternal cascades and shifting pastels, the William Mulholland Memorial Fountain (Riverside Dr. and Los Feliz Blvd.) makes the superabundance of water in this semidesert region seem almost natural. The midcentury-modern DWP headquarters (111 N. Hope St., downtown), surrounded by an opulent reflecting pool, is the picture of confident power.