Your appliance has been designed to be used with tap water.
If you live in an area with very hard water, fast scale build-up may occur. Therefore, it is recommended to mix 50% distilled water and 50% tap water, or to use only distilled water to prolong the lifetime of your appliance.
Do not put perfume, vinegar, starch, descaling agents, ironing aids or other chemicals in the water tank, as your appliance is not designed to work with these chemicals.