What is the RO water profile?

Hey all,

Maybe I'm not understanding something here, but I'm wondering approximately what I can expect for a water profile for the RO water that I can get from my grocery store. I'm guessing it's not completely devoid of minerals, or else there would be no reason for distilled water, but what exactly does RO remove? I can't use my tap water due to a sulfate content of around 250 ppm, and spending 6 bucks every brew to dilute it with distilled and then adding minerals anyway is getting to be a pain. I can get RO water out of the system at the grocery store for a bit cheaper, and in bigger jugs, so I'd like to go that route.

They are both extremely pure forms of filtered water. RO water is cheaper to produce. You can use Carbon/RO filters at home to give yourself a stream of clean water.

I started out using bottles of distilled water, but it's so devoid of anything that my beers were somewhat flat (in flavor). I started using tap water right from the garden hose and was happy with the results.

You could brew any range of pale ales with that water profile. In fact you'd need way more sulfate to properly Burtonize your water.

From what I understand both methods leave behind some things, with distilled being slightly more pure, but not enough to make much of any difference, especially from a cost standpoint.

RO removes 90 - 99% of everything in the water with the rejection dependent on the ion. A check on the websites of people that sell the systems will generally have some data on the particular rejections for individual ions. If your water has 250 ppm sulfate going into an RO system it will have less than 25 ppm coming out.

There will be enough trace minerals in most RO water to support a healthy fermentation as malt supplies surprisingly large quantities of calcium and magnesium. Nevertheless, supplementation of calcium is usually a good idea and adding a bit of zinc (such as the amount found in yeast nutrients) can be beneficial.

When brewing with distilled water (which is much purer than RO water) or RO water you will need some sort of acid to lower mash pH into the desirable range unless you are using a lot of dark grains.

Based on the Ward Labs test I had done on my local RO water source the rejection rate is about 90% whereas most home RO systems are much better. So, you can expect about 1/10th the levels of whatever the local water going into it is.

Since I had my RO water tested by Ward, I included it in Bru'n Water as an example of what the typical concentrations can be. In my case, the source water is from my household ion-exchange water softener. That means that the source water is full of sodium and the calcium and magnesium are low. The resulting product water from the RO system shows the sodium is much higher than the calcium or magnesium, but its still very low (8 ppm). The sulfate and chloride are nice and low, but the bicarbonate is a little higher than them (16 ppm).

The rejection rate for the ions of interest in brewing varies with the diameter of the ion. Divalent ions such as Ca and Mg are rejected better than the monovalent Na ion. So its no surprise to see more Na in the product water than Ca or Mg. If I were to use non-softened water to feed my RO system, the Na concentration would go down a bit and the Ca and Mg would go up a bit. But, they would not be radically different from what is shown in Bru'n Water.

Some more comparative data:

My system uses HF1 polyamide cartridges. These are rated at 98.5% rejection on a TDS basis which they meet. Note that this isn't the whole story. My feed water is about 160 ppm TDS and the permeate 3 or less. I could get that number by removing 157 ppm of everthing else and not rejecting something which contributes the remaining 3 ppm at all. It's clearly not that extreme.

Most places you look list sodium rejection as 92 - 98% whereas most other ions are have listings like 95 - 98 or 96 - 98%. But RO manufacturers are motivated to get sodium rejection as high as possible because

1. RO sytems fed from hard water supplies are nearly always softened first replacing calcium with sodium
2. RO systems are frequently used to clean up briny waters.

I'm not sure what leeway the manufacturers have in this regard (there is art here as well as science) but note that the membranes I use list minimum sodium chloride rejection as 96%.

I went back and checked the specs on the cartridges. 96% is indeed the minimum sodium chloride rejection but typical rejection for NaCl is listed as 98.5%.