There may be numerous causes to why your shower head is malfunctioning. It can have a leak, sediment build-up, or mold. It may simply be getting old or worn down. Leaks can be caused by water supply valves or a loose shower head. On the other hand, sediment build-up is caused by the additives of chemicals in your water supply. Lastly, mold is to be expected from a worn-down shower head since it is constantly connected to the water supply.