Removing kidney stones can be a complicated, sometimes painful process involving medication, surgery or even sound waves to break up the deposits. But preventing them may be as simple as drinking more water.

Kidney stones are extremely common -- about 13 percent of men and 7 percent of women in the United States will get one in their lifetime -- and occur when tiny crystals in the urine (calcium, phosphorus and other minerals or salts) come together to form a hard deposit. Studies have shown that 35 to 50 percent of people who get them will get them again within five years without treatment.

The American College of Physicians this week issued new guidelines for people who have had a kidney stone in the past and they call for these patients to increase their fluid intake so that they can have at least two liters of urine per day. The organization said that there's no difference between tap water or a brand of mineral water but that soft drinks -- such as colas -- should be avoided because they're associated with a recurrence of the problem.

"Increased fluid intake spread throughout the day can decrease stone recurrence by at least half with virtually no side effects," David Fleming, president of the ACP said in a release.

The guidelines also call for other dietary changes. Those who have had kidney stones in the past should reduce their intake of animal protein as well as things like chocolate, beets, nuts, rhubarb, spinach, strawberries, tea and wheat bran because they contain dietary oxalate, which combines with calcium to form stones.