Marshall wrote:My wife, the industrial water treatment chemist, says the culprit is distilled water, itself. Water is a solvent, period. The purer the water, the stronger its solvent properties.

This is true, but being a solvent is not the same thing as being corrosive. Ignoring that distinction and moving on to the real question: will it hurt my machine? Well, given enough time water will dissolve almost anything, and very pure water is a better solvent than mineral water. But as soon as it leaches some metal out of your boiler, its no longer very pure water, and the rate will slow down. I would think that it would take a very long time for significant damage to occur. Starting with minerals in your water won't stop this, just slow it down.

Does your wife have any data on a similar situation that would suggest a time frame in which you would expect to see damage? Not being a jerk here, rather expressing genuine intellectual curiosity. As an engineer I have a pretty good handle on the sciences (at a high level at least) but I can't claim to be a chemist. My water chemistry is mostly what I need to know for beer brewing.

The Water Quality Association writes:

> Typically then, household point-of-use, RO-treated water will still have more than 10 mg/L of TDS, not overly aggressive water

I don't like the taste of RO+DI water (too acidic), but I've found that putting a few small limestones in the jug or tank fixes it. Probably makes it non-aggressive too.

Nate42 wrote:This is true, but being a solvent is not the same thing as being corrosive. Ignoring that distinction and moving on to the real question: will it hurt my machine? Well, given enough time water will dissolve almost anything, and very pure water is a better solvent than mineral water. But as soon as it leaches some metal out of your boiler, its no longer very pure water, and the rate will slow down. I would think that it would take a very long time for significant damage to occur. Starting with minerals in your water won't stop this, just slow it down.

Does your wife have any data on a similar situation that would suggest a time frame in which you would expect to see damage? Not being a jerk here, rather expressing genuine intellectual curiosity. As an engineer I have a pretty good handle on the sciences (at a high level at least) but I can't claim to be a chemist. My water chemistry is mostly what I need to know for beer brewing.

HEALTH: When distilled (or extremely soft) water is boiled in a steam boiler, the ions from the boiler material occupy the vacant space between the water molecules. Water has "space" between its loosely bound molecules that attract ions. This is what solubility means. When water is too soft or distilled there is more "vacant" space which pulls ions from everywhere. When water harder these spaces are not vacant. The rooms are too full with biologically beneficial (let me repeat BIOLOGICALLY BENEFICIAL) ions. Mostly calcium, potassium, phosphorus and other mineral and traces of less harmful metals like iron salts.

When you overly soften the water it becomes like a dry sponge eager to soak up ions from the nest substance it merely comes in contact with. Plastic containers and pipes, metal containers and pipes etc etc. Worst of all is a boiler made of copper. Copper ions easily migrate to soft water (AND TO THE STEAM) just as iron might in a stainless steel boiler. Remember copper is highly soluble and reactive to milk. Steaming milk from steam obtained from copper boiler just screams at me as a warning. Why is no one thinking about this?

The thing is: water is ALWAYS going to have components in it. The idea is to have the most biologically compatible ones. Now we don't want to tax our liver with metal intake do we? I would prefer to work my liver up with some additional alcohol instead

When you steam milk, only chemicals with a lower vaporization point than water will be present in the steam. All the beneficial minerals and non-beneficial ions will be left in the boiler.

Hi Chris
Steam will carry quite a lot of the soluble contaminants in the water + boiler + heating element used to boil the water. Yes it is true that considerable amount of particulate impurities such as precipitated carbonates, and dirt will be left behind but ionic particles can be carried with the steam. Please google. Boiler plant chemistry is a major branch and engineers do specialisations in boiler material chemistry to achieve pure steam.

Coffee machine boilers are held at higher pressures and are not comparable to simple distillers (like alcohol distillation) and therefore the vaporisation points are less significant in this instance.

Here is an article from Wikipedia for reference: (several such articles are available if you search) Copper ion contamination in steam is a major issue in industrial steam generation for turbines etc.

http://en.wikipedia.org/wiki/Ultra-high ... _annealing

Hope this helps.