what is the ph of RO water
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FermentNEthinG
Well-Known Member
mine runs @ 7.0 +\- .1
2 ppm's!
2 ppm's!
As R/O retains some small mineral content it will vary be the source water and the efficiency of the membranes and the rejection rate. My source water is over 750 TDS, and the R/O water measures about 72 TDS. My pH is currently holding between 6.3 and 6.5 at room temperature. With 8 gallons, just a few ml of 10% Phosphoric brings that standing pH below 6.0. I would assume the lower TDS the source, the closer to 5.5 you could expect... And more sensitivity to acid/base additions. I believe I have read somewhere that in a 99% efficient R/O the theoretical pH ( no idea at what temperature) is 5.5. That may actually be R/O with DI staged. Can't remember.
It depends on, as you can see from the answers, the residual mineral content of the water and its exposure to atomospheric CO2. At 0.0003 atm partial pressure of CO2 the equilibrium pH for pure water is 5.57. I just measured my RO (TDS meter says 1 ppm but I haven't recalibrated it) at 5.63. If the reason for the question is curiosity that's fine but if you think there is a practical effect on your mash pH, there isn't. What counts is the alkalinity and the alkalinity of RO water is very small.
It's actually more complicated than AJ mentions. Since dissolved gases are virtually unimpeded by the membrane, they are typically present at elevated concentration in fresh RO water. Many municipal RO plants run their product water through air stripping towers to help release those gases and reduce the potential for low water pH. A prevalent gas is often CO2. I had a brewery client that failed to vent off the CO2 and ended up producing thousands of gallons of very tart beers with their RO water. They went out of business because they had to waste that beer. They didn't call me soon enough.
GotPushrods
Well-Known Member
Glynn said:
You don't. You need to give it the alkalinity. I know it seems a bit counter intuitive, but the pH itself is pretty irrelevant. Alkalinity is a direct measure of the amount of acid needed to reach a target pH.
michaeltrego
Well-Known Member
My last Ward Labs report showed RO at 7.8 pH, TDS 26, Alkalinity 3. On a recent Munich Dunkel brew day, it was the first time I checked pH throughout the whole process: RO 7.4, mash 5.4 (thanks to Bru'n water's help), preboil 5.5, postboil 5.2.
Wierd story. I guess it's obvious they didn't have an atmospheric tank but how did the gas stay entrapped during the heating and stirring of the mash tun, the exposure to air in the lauter tun and especially the boil? Is (or was) the entire process done under pressure (brewery in the Rockies)?
There are even more complications. Hydronium ions pass through preferrentially to hydroxyl ions so there is a slight additional reduction in pH from that.
Pure water has an alkalinity of about 1.5 ppm as CaCO3 WRT pH 4.3. Given the alkalinity is so low it doesn't much matter what pH you feed into a calculation so just use 7. Even though RO water isn't pure the alkalinity is still going to be very low (e.g. the data in #8). It still doesn't matter much what pH you specify in such a case (within reason) but if you have measured it you might as well use that value.
Is there a ball park average that i should set my alkalinity to. I don't plan on having the water tested and don't have any problems hitting my mash numbers. My mash eff is always around 80 %. Right now the numbers im using are the ones i found on the list of water on the bruin water page
ca 1
mg 0
na 8
so4 1
cl 4
bicarb 16
ca 1
mg 0
na 8
so4 1
cl 4
bicarb 16
Those are the numbers that I use with good results.
If bicarb is really about 16 then alkalinity is about 13 but I hope your system produces less than that. Feed with 100 and 95% rejection would run 5 (plus the 1.5 of the water itself). If you use a number high by 10 you'll calculate 0.2 mEq/l more acid than you need e.g. 4 ml more 1 N acid than necessary in 5 gal. This still won't make much of a difference in mash pH I always use 1.5 for. RO - same as DI.
No system here, I use store bought RO water. I'm going by the horseshoes and hand grenade method of brewing here
. That's why i was interested in ball park numbers I don't have the time, desire and financial resources to get anal with this. I'm very happy with the results I'm getting now with RO water compared to what i was making. It's made a vast improvement in my beer. I'm more or less looking for validation that I'm basically on the right track.
. That's why i was interested in ball park numbers I don't have the time, desire and financial resources to get anal with this. I'm very happy with the results I'm getting now with RO water compared to what i was making. It's made a vast improvement in my beer. I'm more or less looking for validation that I'm basically on the right track.The problem with doing this with store bought stuff is that some stores add minerals back in to add some flavor to the water - really low TDS RO water tastes pretty flat. If it isn't too much trouble perhaps you could ask the vendor whether he is doing that or not. Another possibility is to buy a TDS tester (they are really inexpensive) and get a feel for what the ion content is. If the water measures less than 5 TDS you could use 1.5 for the alkalinity. If it measured 10 - 40 you could use half the TDS etc. These are still WAGS but if the TDS reads low at least you have the comfort of knowing that it doesn't much matter.
I don't know if any minerals are being add back in. I'm not using the water from the machine in the store because I don't trust them to maintain it. I've been buying pre bottled 2.5 gal jugs that are brought in. I tried looking up info on the water but came up with nothing.
With such a little amount of alkalinity, your hand grenade concept, in my opinion, works fine. Just be aware that switching brands or over to spring water will require different considerations. Just keep good enough notes that if you wish - you can rebrew that recipe with the water and additions. Sounds like you have already had good results with the Bru'n Water default numbers.
I have been playing around with my water report reduced by the efficiency of my RO system in Bru'n Water, which results is very slightly different mineral amounts. I have not brewed that way yet. AJ or Martin, is that one way to approach this? I can measure the effectiveness with TDS measurements before and after RO, then reduce my water report by that percentage? Since I have ridiculously high alkalinity and sodium, I still have above 70 PPM reading.
I have been playing around with my water report reduced by the efficiency of my RO system in Bru'n Water, which results is very slightly different mineral amounts. I have not brewed that way yet. AJ or Martin, is that one way to approach this? I can measure the effectiveness with TDS measurements before and after RO, then reduce my water report by that percentage? Since I have ridiculously high alkalinity and sodium, I still have above 70 PPM reading.
Yes with some attention to details. If you have very hard very alkaline water I assume your RO system is fed from a softener. In this case you would have to recognize that magnesium and calcium are replaced by equivalent amounts of sodium and use that equivalent sodium level reduced by the rejection of sodium and 0 for calcium and magnesium. Seventy is pretty high TDS after RO but a lot better than 1400!
