I've used Rowenta irons for many years; distilled water has always been a "no-no" for their irons, although the Rowenta pressure iron and steamer booklet says that if I use tap water, which is harder than 12 grains (who knows????), they recommend mixing half tap water and half distilled to reduce the hardness. They go on to recommend using bottled spring water entirely, but "NEVER use 100% distilled water as this can cause the iron to spit and leak."