Is RO (reverse osmosis) water drinkable? Busting some of its myths and reiterating some of its truths

RO (reverse osmosis) water used to be all the rage 10-20 years back. Heck, you almost found RO in every water treatment device in the domestic market! You would surely be forgiven for believing that RO WAS the only water treatment available for the consumer.

Well, the rage has quieted down somewhat now. We see a lot of other water treatment methods nowadays - UV, microfiltration, ultrafiltration, activated carbon and specialty (usually means proprietary with little information given to the consumer) filter medium.

Why the declining interest in RO? I suspect that both suppliers and consumers are waking up to the drawbacks of RO, both real and perceived.

(In this post, I am talking about freshwater RO in the home. Seawater desalination as a water utility also makes use of RO but there are many important differences. See my previous post for more information.)

Myth 1: RO Water is too pure and doesn't provide minerals for the body

One thing I have to admit is RO is so darned good at removing "impurities" from water. Impurities include beneficial minerals needed by the human body and/or for aesthetic considerations. Some of my personal sources swore that mineral water tastes much better than bland old distilled water. (Like RO, distillation can remove lots of impurities too.)

Without going into math, we are better off getting our mineral intake from our food rather than water. Look at it this way, the concentration of minerals in water (even mineral water) is miniscule. You have to drink a hundred litres or more per day to get your recommended dose. Furthermore, if you talk to a dietician, she will convince you that the chemical nature of minerals is food makes them easier for absorption into our bodies.

Myth 2: RO Water leaches minerals from the body

Continuing on the logic that RO water is so pure, some pointed out that its drinkers will experience the double whammy of not getting their dose of useful minerals, as well as having the existing minerals in their bodies leached out by the RO water passing through their digestive tract.

One, the biochemical condition in our bodies is constantly maintained (aka homeostasis) or our bodies will simply not work. The mineral content in our bodily fluids is especially stabilised by our kidneys which control the amount of minerals wasted into our urine. Sorry, minerals do not simply leach into our digestive tract.

Two, sailors have been drinking RO water on a long term basis on board ships and submarines. We have yet to see any evidence of adverse effects.

Fact 1: RO "wastes" part of your water input

To me, this is significant no-no for water treatment. For every litre you feed into RO, you only get half (can be more or less depending on various factors) of it as treated output (aka permeate). The other half is known as retentate or concentrate and disposed.

Sure, the concentrate from a domestic RO unit probably is only 30% or more concentrated compared to the feed but no one in his right mind will want to drink it as it totally defeats the purpose of RO in the first place. And sure, you can use this concentrate for other purposes e.g. irrigation, washing. But to me, that does not change the fact that you are only getting half the water for drinking.

Fact 2: RO is an overkill

For those who have not read my practical guide on 3 Critical Questions on Choosing Your Water Filter, I suggest you visit the link, download it (it's free!) and sit down to read it.........

Finish reading? If you haven't, here's the short version. Basically, before settling down on a water filter/purifier/treatment unit, you have to do some homework, specifically, know what impurities are of concern to you, what levels are they at in your raw water and whether your chosen treatment unit can remove them down to "safe" levels.

RO is an expensive (you need to pay for the high energy usage to generate the high pressure inside) and wasteful (see fact 1 above) water treatment method unless you have no other choice to remove your impurities of concern. Sure, the water output is pretty pure but most of us do not need that kind of purity unless you are manufacturing pharmaceuticals or electronic wafers in your home. Heck, coffee and tea should not use this level of purity as various sources have claimed that a higher mineral content is needed to bring out the optimum taste in them.

Figure: Typical RO system incorporating other water treatment methods. RO is never stand-alone. The entire system tends to be rather bulky so you have better allocate enough real estate to keep it.