The Sierra Club is suing the city of San Francisco’s water department, claiming officials are manipulating water data to justify bigger water grabs for the city — and causing unnecessary harm to the environment, and inflating customer rates. The suit, filed last week in San Francisco Superior Court, calls for the San Francisco Public Utilities Commission to revise its state-mandated Urban Water Management Plan to reflect more modest water needs, notably from the Tuolumne River at Yosemite National Park, where the bulk of the city’s water comes from. … The agency has previously maintained that its extensive water diversions and conservative water plans are necessary for sustaining the Bay Area, its people and its booming economy. … The Sierra Club’s legal challenge … comes at a time when San Francisco’s water supplies could be increasingly constrained, not just by climate change and drought, but by a landmark proposal by the state, known as the Bay Delta Plan update.