Three textures of soft Elements cleaning cloths should be part of your cleaning ritual for your fitting. Wiping them down after every use will stop hard water from damaging the finish.
The expectation is that the original lustrous finish on beautifully crafted fittings will last at least 20 years. This is essentially true unless the finish meets with some calamity such as an ammonia based or abrasive cleaner or poor air quality. In fact, the fitting should be treated with the same care as one would devote to the finish of a fine piece of furniture or a well-loved car. Improper cleaning can damage the surface of the fitting and careless upkeep is a sure way to allow air, water and harsh chemicals to ravage the plating.