Southern Californians who reside near the mountains, hillsides or canyons live with the risk of a wildfire burning down their homes. But rarely do they think about a fire contaminating their drinking water. Perhaps they should. Just ask residents of Ventura, Santa Paula and Ojai, who must boil their tap water before drinking it, cooking with it or brushing their teeth, the result of the powerful Thomas fire that knocked out portions of their water system Tuesday and grew to 96,000 acres by Thursday.