QUILLAGUA, Chile — During the past four decades here in Quillagua, a town in the record books as the driest place on earth, residents have sometimes seen glimpses of raindrops above the foothills in the distance. They never reach the ground, evaporating like a mirage while still in the air.

What the town did have was a river, feeding an oasis in the Atacama desert. But mining companies have polluted and bought up so much of the water, residents say, that for months each year the river is little more than a trickle — and an unusable one at that.

Quillagua is among many small towns that are being swallowed up in the country’s intensifying water wars. Nowhere is the system for buying and selling water more permissive than here in Chile, experts say, where water rights are private property, not a public resource, and can be traded like commodities with little government oversight or safeguards for the environment.

Private ownership is so concentrated in some areas that a single electricity company from Spain, Endesa, has bought up 80 percent of the water rights in a huge region in the south, causing an uproar. In the north, agricultural producers are competing with mining companies to siphon off rivers and tap scarce water supplies, leaving towns like this one bone dry and withering.