Sorry folks, but drinking deionized water in and of itself will not hurt you in the slightest. The idea behind this is an inappropriate extrapolation from laboratory science. Extremely pure water has a large capacity to dissolve ions from various containers that it's put into, which is why if one puts 18.3 megaohm laboratory grade water into a glass vessel, the resistivity will quickly drop into the 0.5-1.0 megaohm range. That's partly from the adsorption of CO2 in the air, but also dissolution of sodium and silica from the vessel walls itself. And if you keep highly pure water in a 316 stainless steel system that's not "passivated", you will get corrosion of the steel walls as a very tiny amount of it dissolves into the water (this is called "rouging").
These effects have led some to inappropriately assume that highly purified water is "corrosive" and that it will remove minerals from your body as they dissolve into the water if you drink it. There is a rather serious logical problem with this assertion, which is that your stomach contains a massive amount of electrolytes compared to what is required to make highly pure water into "normal" water. It's true that if you only drank highly purified water and your food was deficient in minerals, then at some point you might develop a mineral deficiency. This is often cited as evidence that drinking highly purified water is "bad for you". What alarmist websites that espouse this dreck aren't telling you is that you would likely develop the same mineral deficiency regardless of whether you were drinking "normal" water or highly purified water. And for the average person in developed countries, the vast majority of your daily mineral intact is from food, not water.
However, there are several reasons not to drink water from your average hobbyist's RODI system, though it has nothing to do with the water that's produced being inherently bad for you. The first is taste - a lot of what we perceive to be "good tasting water" comes from the minerals that are in it. Highly purified water tends to taste "flat". This is why, btw, that bottled water companies use RODI systems to purify the municipal sources of water that they use, then add sodium, calcium and magnesium salts back into it before they bottle it. The second reason not to drink hobbyist-produced RODI water has to do with sterility. Municipal sources add chlorine/chloramine to water for a reason, and that's to prevent you from getting a bunch of live pseudomonas and escherichia (among other genuses) when you get a drink of water from the sink. In a hobbyist's RODI system, the carbon blocks remove the chlorine/chloramine, so the rest of the system downstream from the pretreatment stage can definitely grow several types of problematic bacteria that you wouldn't want to drink.
That's why RODI systems that are used for manufacturing beverage products have 2 additional controls in the system, which are UV sterilization and ultrafiltration. These systems are also regularly sterilized with peroxide-based sterilants to prevent the growth of biofilms.
Bottom line - if you want to use RODI in an application were it will be heated/boiled, there's no reason not to. But don't drink it straight from your RODI system without adding in some additional components to ensure its microbiological safety.
www.reef2reef.com
