Farmers, though, don't keep track of the water they use. The DNR figures its nearly 20,000 agricultural water-use permits closely reflect the number of irrigation systems out there. It's the single largest user of groundwater. Farmers water during the growing season. For their biggest crops, that's about six months.
Some big farms use as much water as medium-size cities.
The need to measure agricultural water use was clear by the mid-'90s, McLemore says. So the state asked UGA's College of Agricultural and Environmental Sciences to devise a project to monitor a statistical sample of the irrigation systems. USGS has good planners in Atlanta, but doesn't have a local presence, close to the farmers. The college, through the Extension Service, does have that local presence. Agents in every county work daily with farmers and have close links with college engineers and other scientists.