You are having one of two problems. These faucets have a cartridge that slides inside a cylinder. Something in the water may have dissolved the existing lubrication. Open the cylinder and apply some vaseline. The other possibility is that if your water supply is rich in iron, there may be a buildup of the metal inside the faucet system. You can tell if this is happening because water exiting the faucet will have a red tint to it. If this is the case, correcting the problem is simple enough. The cartridge inside the faucet needs to be replaced and the cylinder in which it slides should be rubbed with some steel wool. It is not very expensive and if you are worried about having the right part after you have left the hardware store, take the cartridge that you have into the store with you.