gaigai,
we have very hard water here. I've used both distilled & tap water without issues on 2 different Rowenta irons. They work well for years.
I think there may be cleaners recommended for people with hard water who use tap in their irons, though I've not purchased. Some irons (including Rowenta) suggest tap because they are designed to handle hardwater up to a specific point. We don't know our exact hardness and treat with a softener, so technically, we're not supposed to be able to use tap only....but I do, without issues.
I'm glad you are happy with your iron but I'd prefer not to pay for water just for an iron. My last Rowenta lasted about 12 years with regular use and admittedly a couple of drops to the basement floor. I suppose I need this brand due to my clumsiness factor alone. =)