A faulty shower diverter causes water to flow from both the tub spout and shower head simultaneously. For pull-up diverters on the tub spout replace the entire spout by unscrewing it counterclockwise. Wall-mounted three-handle diverters require replacing the internal stem and washer. Turn off water supply remove the handle and unscrew the stem. Take the old parts to the hardware store for exact replacements. Apply plumber tape to threaded connections during reassembly.