Why does a tub spout leak. Brand new combo shower tub valve and tub spout. Will slowly leak over a few days before completely dries out, about a tablespoon. The plumber came back and replaced the cartridge which did not stop the leak and did not know what else to do. Is this normal? The water here is very hard, if left unattended for any length of time the tub will stain. Is this excess water left over from the shower? Why would it take such a long time to drain and why doesn't the tub spout diverter hold the water?