Your appliance has been designed to work with tap water. If your water is very hard, mix 50% tap water with 50% distilled water (available in stores).
Do not use rainwater or water containing additives (starch, perfume, aromatic substances, softeners, etc.) or water obtained through condensation (e.g. dryer, refrigerators, air conditioners or rainwater). These contain organic waste as well as minerals that condense under the influence of heat and cause sputtering, brown stains or the premature wear of your appliance.