There are several reasons why waterproof boots may leak. The most common reason is that the boot is not made of waterproof material, or that the boot has been damaged and is no longer watertight. Other possible causes include a poor fit, improper care or cleaning of the boot, or wearing the boot in extremely wet conditions. If your boots are leaking, check to see if they need to be replaced or repaired. You may also want to try a different brand of waterproof boot.