The purpose of this research study is to determine whether the combination of inhaled amiloride and a concentrated salt solution is better than the salt solution itself for cystic fibrosis (CF) patients. In CF, airway secretions are thick and dehydrated. Many patients use inhaled salt solutions to help draw water into their secretions so that they are easier to get rid of with chest physiotherapy (“chest PT”) and cough. Unfortunately, these salt solutions are reabsorbed very quickly by the airways, so the beneficial effects may not last very long. In the hopes of prolonging their effects, the drug amiloride could be used in combination to slow salt and water reabsorption from airways. Amiloride is a medication that has been given by mouth for high blood pressure for many years. It is possible that the combination of salt solutions and inhaled amiloride may significantly improve the clearance of secretions in CF, which would be expected to improve lung function in CF.