Among the changes ahead when Democrats take control of the House in January, add this one: The switch will upend the balance of power in California’s water wars. In the two years since Republicans’ 2016 election triumphs, party members from the Central Valley led by the current House majority leader, Rep. Kevin McCarthy of Bakersfield, have gotten several water bills for their area through Congress. Those included the first significant California-specific policy in decades, as part of the Water Infrastructure Improvements for the Nation Act, also called the WIIN Act.