Housing advocates and developers are warily watching California’s intensifying drought and what it may mean in a state that needs millions of new homes to house its residents. Eighty-five percent of the state is in extreme drought. And in coastal Marin County, north of San Francisco, rainfall is at its lowest levels since records began 140 years ago. It’s here where the state’s twin issues of housing stock and water availability are colliding. But it could be a harbinger of things to come for the rest of the state. Additional housing puts more stress on water supplies.