We've never had a problem with hard water scaling our Rowenta irons, but we are on our third (in 15 years) due to the first two *rusting* internally.

Distilled/RO water will not boil at a noticably higher temperature than tap, at most around 2 degrees difference. This shouldn't affect the iron's operation. As for dripping/spitting, I don't know why it might occur with distilled and not tap water. There are 'superheated water' phenomena than can cause such effects, but they are no different with distilled water than with tap water.

In the world of semicommercial espresso machines, distilled water is often a problem because the fill sensor works on electrical conduction, which needs a touch of minerals in the water. One common solution is to add a tiny amount of tap water to distilled or RO in the tank, just enough for the sensors to work. - DR

I have seen the Rowenta demonstrated on QVC many times (and I have owned one for many years) and the woman on QVC says that you should use tap water, but not softened with salt. I use spring water from the grocery store, and have no problems with it--buy it by the gallon.

Well, the answer from Rowenta and dross are not entirely correct.
Distilled water does NOT have a HIGHER boiling point than tap or spring water. In fact, the opposite is true. Impurities and minerals increase the boiling temperature of liquids. Look up "distilled water" and "boiling point elevation" on wikipedia.org. Any liquid can be "superheated", the impurities of tap water don't make a significant difference in that regard.
The last part of dross' explanation makes much more sense. Distilled water doesn't conduct electricity, so that could be a problem for the sensors. The pH value of distilled water is generally also lower than the pH of tap water, but that shouldn't be enough to cause any damage to appliances. It sounds as if the new irons use some sensors that rely on medium water hardness.

The conductivity thing makes the most sense. The answer from Rowenta doesn't seem particularly logical to me. No trouble buying bottled water. Just curious about the actual reasons.

Thanks to all for responding.

Sometimes distilled water and RO water are termed "agressive". Maybe a chemist in our midst can explain this correctly, but I've been led to believe that water really wants to have some mineral component in it's make-up and the total or near total lack of this in distilled and RO water will make it attack metals it comes in contact with. Maybe Rowenta is concerned about this effect or maybe if the inside of the iron is kept too clean they won't be able to sell you a replacement soon enough :-)

Looser - is the slightly acidic nature of this water the same as calling it agressive? Does this have something to do with water's ability to disolve stuff until it comes into some sort of balance?

I know from previous work with pumps/valves that distilled water is, indeed, very "aggressive". We sold specially coated valves and fittings to firms that had distilled water lines for that reason. Worse when its hot.

All I wished was to receive a response from Rowenta that made sense. No problem complying with their instructions (its a really nice iron!) but I do wish I understood what the actual problem was.

gordonr - Water is known as the universal solvent because many substances readily dissolve in water and most will dissolve at least to some extent. However, a given amount of water will only dissolve so much. Just to make it easier, assume on liter of water can hold 100 grams (not correct and very simplistic, but useful for explanation) of anything. If it already has 75 grams dissolved in it, it can only dissolve another 25. If it has 0 grams dissolved, it has a 100 gram capacity and will be more aggressive. The mild acidity of RO or distilled water is because of its purity.

Water with a bit of hardness will form a thin film of scale on the heated metal parts of the iron, protecting them from corrosion. Water with too much hardness will form a thicker scale, eventually causing the heating elements to burn out. The scale acts as an insulator, forcing the element to burn hotter in order to provide the same temperature water.

The answer of aliceinwonderland_id is pretty accurate. Pure water like distilled or RO water is not anything that occurs naturally. Nature tries to keep a balance of concentrations. Pure water therefore is somewhat aggressive in trying to dissolve minerals or metals. The reason for the acidic nature of pure water is the fact that carbon dioxide from the air gets dissolved in water and forms carbonic acid. In theory, very pure water would have a pH of 7 since there aren't any ions present. In reality, it dissolves a lot more CO2 than tap or spring water so that its pH is quite a bit lower.
Over a long time and by repeatedly heating it up to its boiling temperature, it is possible for distilled water to cause damage to the heating element.

Highly distilled, very pure water will attack rubber seals, O-rings, and gaskets. Saw this happen to a water-cooled spacecraft once. :-O

Thank you so much for this post! You answered a lot of questions I had about the water to use. My husband insisted that distilled water was the best to use and that is what I had been using in my Rowenta Iron. However, it was spitting and leaking and I was getting browning on my ironing board cover and on my cotton iron rag. I was also getting what looked like black rust type deposits on the base of the iron that I was able to scrub off with Ajax and a SOS pad. You answered my questions and now I am going to get some Spring Water for the iron. I do a lot of sewing and need my iron on as often as my sewing machine, which is hours and hours almost every day. I just hope that the distilled water did not hurt my iron. I love my Rowenta Iron!

Susan

Here is a link that might be useful: Raisin Toast

I just sent a Rowenta back for repair and was sent a replacement. They told me to use distilled water. The whole thing doesn't' make any sense. the iron still leaks.

Any suggestions on what doesn't leak?

I use spring water which I buy at little kiosks in our community for 25 cents a gallon. I don't have problems with spitting, unless I forget to push the little lever to steam. I love the Rowenta irons.

I was just having this dilemma with my new Rowenta. I have very hard water (25 grains), softened water (whole house softener), and RO water. I called Rowenta and they said RO water was fine, but no Brita filtered water and no distilled water. Further checking, though, tells me that you're right; RO water is also "aggressive". I guess I'll be mixing a little hard stuff from the cold tap in there. No way I'm going haul spring water for my iron!