Business Report: On the cracked, grey clay of an ancient lake bed on the edge of Australia’s outback, Guy Kingwill is at the frontier of a global rush to commercialise water. Despite a long drought, Kingwill, who runs the vast Tandou farm, 142km from Broken Hill, has just sold his property’s vital water on a national market rather than pump it into irrigated cereal crops. “The return on the water is higher,” Kingwill says. “Where we are it’s broadacre cropping. But the market now is driving …