After one year of torrential respite, drought may have returned to California, and with it, a renewal of the state’s perpetual conflict over water management. State and federal water systems have told farmers not to expect more than a fifth of their paper allocations, the state Water Resources Control Board is weighing a new regime of mandatory conservation, and supporters of more reservoirs are complaining about the glacial pace of spending $2.7 billion set aside in a water bond for more storage.