A vote Tuesday added $9 per acre to the cost of water in the Modesto Irrigation District. Its board decided 4-0, with Director Janice Keating absent, to adopt the increase for the irrigation season that just began. The extra money will go to maintaining canals that deliver Tuolumne River water to about 3,100 farmers. Under state law, the proposal would have died if a majority of them filed protests at or before Tuesday’s hearing. Only 11 did so.