More farmers in drought-stricken California are using oilfield wastewater to irrigate, and a new panel on Tuesday began taking one of the state's deepest looks yet at the safety of using the chemical-laced water on food crops. In the fourth year of California's drought, at least five oilfields in the state are now passing along their leftover production fluid to water districts for irrigation, for recharging underground water supplies, and other uses, experts said.