Two somewhat-related water questions I’ve received recently ~
Ok, not really all that related, but they both have to do with water, so two birds with one and a half stones, right? Something like that. I haven’t thought much about chemistry lately so I thought I’d take a stab at these two - for the basics of each type of water, click the italicized title.
Heavy water: Heavy water is also known as deuterium oxide, and is formed by using deuterium rather than “normal” hydrogen. Deuterium is an isotope of hydrogen that is stable and naturally-forming, but which has a neutron in its nucleus - “normal” hydrogen [protium] has NO neutron in its nucleus. Because D2O contains two more neutrons than water made with normal hydrogen, it’s about 11% more dense. Note the ice-cube graphic - in “normal” water, a “normal” ice cube floats, but a deuterated ice cube sinks.
Though D2O (and semi-heavy water, with just one deuterium - HDO) occurs naturally on earth, it’s extremely uncommon. However, due to its increased density, it was one of the first effective “moderators” for nuclear fission reactors, and it was extremely useful in the separation of plutonium for nuclear weapons, so entire plants were set up to separate “heavy” water from normal water.
These days, deuterium oxide is not widely used outside of the inorganic chemistry and nuclear physics world, and is no longer commonly used as a neutron moderator in fission reactors. If consumed, it’s considered moderately toxic, but it’s not going to kill you unless it’s all you drink for a very long time, and at $300/kg and a controlled supply chain (since using it is part of the easiest process of creating a nuclear bomb), good luck with that. I mean, not really, don’t go drinking it on purpose, just don’t think you’ll die if you have a deuterium cocktail.
De-ionized water: Long story short, no. There are no tangible, or even plausible, health benefits to either de-ionized, or "super-ionized" water, at least over any municipal tap water.
De-ionized and reverse osmosis (DI/RO) water is just water with its ionic mineral salts removed (in various fashions) - things like calcium, copper, bromide, and iron, which build up in the water while it’s on or under the ground, and sometimes while it’s in storage containers. Those salts are part of what makes water “hard”, which can lead to mineral buildup on faucets, tubs, or in machines that use water.
While de-ionized water can prevent hard water buildup, you don’t want to use it as a substitute for “regular” (even just regularly distilled, but not deionized) water in situations where there’s a possibility that the minerals in the water are not being acquired in other situations, such as in famine conditions, and on ships. The WHO recommends avoiding demineralized or deionized water unless it’s the only possible clean water source.
Personally, the lab I worked at used Milli-Q (ultrapure - RO/DI + ultrafiltration) water for our coffee machine, because the local water tap water was really hard and left limescale buildup in the drip. We already had the Millipore machine, so we figured it didn’t hurt. There were no health benefits or detriments to doing so, just less effort when trying to clean the coffee machine.