This is a pretty complex subject, and it is difficult to make generalizations because of the differences in efficiency of the various methods as well as the differences in the feed water. (95% reduction of the feedwater, so the quality is going to depend on how contaminated the original water is...) One reference mentioned the illnesses associated with cruise ships and RO, eventually bacteria breaking thru. People like to use charcoal filters on their drinking water, but if you don't change them out on a regular basis you can end up with worse water than you are treating. One person I know was advised to drink distilled water by his doctor based on the conductivity of his urine, but I was always told that it was unhealthy to drink pure water because it removes the electrolytes from the body. One item found on a search talked about how great tasting pure water was, but actually I think it is totally devoid of taste, as it is the minerals in the water that impart flavor. I was a Chemical Engineer at a supercritical power plant, and in charge of the demineralizers that processed the feed water. A supercritical boiler operates at 3600 psi and 1000F, and is a once thru boiler, i.e., everything in the feedwater goes thru the turbine. When you say demineralized water, that can cover anything from a single bed mixed bed deionizer to multiple beds, the one at the plant consisted of statified bed cation units, then it passed thru a vacuum degasifier to remove CO2, then anion units, then a mixed bed. The water coming out of it was as pure as can be made on a large scale system (up to 600 gpm). When you distill water typically some of the impurities get carried over with the steam, it varies with the volatility of the individual impurities and the pressure. In other words, not all demineralized (or deionized or demineralized) water is the same. An easy test is to use conductivity, we produced water that had a conductivity of 0.055 micromhos if I recall, or greater than 18 megohm water. (conductivity is the reciprical(sp?) of resistance...) All of this is subject to the fraility of my 65 yo brain..... Is everyone dozing off yet???