Okay, technically you can lose weight, but it would take gallons and gallons of ice-cold water to burn one measly pound, making its practical application zilch.
The theory is that your body has to expend calories to warm the water up to body temperature before it’s digested, so the colder the water, the more calories you burn digesting it. “It takes one calorie to raise a liter of water one degree centigrade,” explains Allan Green, Ph.D., an obesity researcher at Bassett Research Institute in Cooperstown, NY. “If you drink a liter of water that’s two degrees centigrade and it needs to rise to 37 degrees [body temperature], you’d burn 35 calories. A pound of fat is 3,500 calories, so you’d have to drink 100 liters, or about 25 gallons to burn one pound of fat. But that doesn’t take into account the extra trips to the bathroom.”
That said, it certainly can’t hurt to drink ice water in place of warm water (and definitely in place of soda or juice). After all, a calorie burned is a calorie burned, and it all adds up. But don’t count on gaining a sleek figure by only switching up your water temp.