Single-handle shower faucets are becoming more common in homes due to their simplicity and durability. A loose shower handle will usually occur well before the shower actually becomes worn enough internally to drip, so repairing it sooner rather than later is always a good strategy. The two most common shower faucet types use either an internal ball mechanism to mix and direct the water, or an internal cartridge to mix and direct the water. In both cases, this diverter mechanism is what the shower handle is attached to. Both types of faucets are relatively easy to fix. Following a few simple steps will save the expense of hiring a plumber.
Locate the shower water shutoff valve inside the tub or shower access panel. Shut off the water supply to the shower. If you cannot find that valve, shut off the main water supply to the house.
Release the water contained in the shower head and pipes by opening the shower faucet slightly and letting the water drain. If the water supply was cut off properly, the shower will stop dripping completely in under a minute.
Remove the loose faucet handle. All shower faucet handles will have a set screw which holds the handle in place. Most are concealed, so look carefully around the sides and top of the handle and locate it. Using a screwdriver or adjustable wrench, remove the set screw.
Pull the shower handle straight out from the faucet housing. Inspect it thoroughly to help determine what caused it to be loose. Use a rag to clean the insides of the handle, and look to see if the teeth inside the mounting hole on the shower handle are still sharp, and not stripped. If the teeth are stripped, the handle must be replaced.
Check to make sure that the shaft (on the shower assembly) that holds the shower handle is completely tight. If it's not tight, tighten it using an adjustable wrench. Do not overtighten, since this is the component (diverting valve) that contains the cartridge/ball assembly that directs water flow and it may leak.
Inspect the teeth on the diverter valve protruding from the shower assembly that you just tightened. If the teeth are worn or broken, then the ball/cartridge diverter valve must be replaced.
Reattach the shower handle, making sure it is fully seated on the diverter valve shaft. Tighten the set screw, making sure that the handle retains its normal range of motion. Turn on the water supply and test the faucet's operation.