My urologist says that the water and citric acid in lemonade help prevent kidney stones. Is he right? —D.M.L., Wiley Ford, W.Va.

Yes, about the water. The best way to prevent kidney stones is to drink plenty of fluids, particularly if you have a history of stones. Avoiding excessive sodium and eating plenty of fruits and vegetables can also help. If those steps fail, raising the level of citrate (citric acid) in the urine can also impede stone formation. But while lemonade and other citrus juices can increase urinary citrate, they probably don’t provide enough to reduce the risk of stones; in fact, grapefruit juice may increase it, for unknown reasons. However, citrate pills, such as prescription potassium citrate (Urocit-K), are effective. Or your doctor may suggest another drug, such as allopurinol (Zyloprim) or hydrochlorothiazide (Esidrix, Hydro-DIURIL), that prevents stones in other ways.