in the nearby town of cuicatlan, a living example for the effects of irrigation can be seen. cuicatlan is located in the tehuacan valley, an arid region of mexico with insufficient rainfall for successful agriculture. but the town has abundant water, thanks to a nearby river. harnessing this forceful river is the matamba dam. the dam diverts water into a central canal, which winds down the mountain side on a journey 15 miles long. along the way, a canelero, or a canal keeper, opens a sluice gate to send water into a network of smaller feeder canals. below, a farmer waits to irrigate his cornfields. farmer: el agua es la vida porque... interpreter: water is life. because without water we cannot farm. that's why we say water is life. having water, we're happy. we can sow any plant we want -- the beans, the tomatoes, the chile, melon -- all because of water. keach: the irrigation system at cuicatlan has increased food production dramatically, but it has also brought with it a need for administration. anthropologist bob hunt is an expert on how irrigation affects the way we organ