Grant Davis, general manager of the Sonoma County Water Agency, was tapped Wednesday by Gov. Jerry Brown as the state’s new director for the Department of Water Resources, handing a veteran of North Bay politics and water policy a central role in Brown’s controversial bid to overhaul California’s water system with a $17 billion pair of tunnels under Sacramento-San Joaquin Delta. Davis, 54, has led the county Water Agency since 2010 and is set to begin in his new post in Sacramento in August, pending confirmation by the state Senate.