After performing leak detection I was unable to determine that there was any leaks on the water system. I listened to manifold and angle stops and could not hear anything. Checked meter for several minutes and meter was not moving which is a good indicator that there is not a leak on the water system. Inspected behind units bathtub via access panel. Noticed the drain basin was full of water. Ran water in the tub and immediately water started flowing out from the over flow. Replaced overflow drain and gasket to stop leak. Explained to manager to keep an eye on the unit and the moisture in the walls and carpeting in the bedroom continue then to let us know.