By Dan Whitcomb LOS ANGELES (Reuters) – Some 6 million residents of Southern California are being ordered to water their lawns and gardens no more than once a week, the Metropolitan Water District said on Wednesday, citing the state’s historic drought. The order affects some of the most populated areas of Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties, although it does not apply to all parts of all the counties. Metropolitan Water District officials warned residents that if they did not comply with the first-of-its-kind order, which will be enforced starting Jun…