Help with RO Water - II

[Peebee]

A second go at this 'cos I didn't gather any useful way forward from the first. Perhaps the resident RO Water guru (@Buckeye_Hydro) has my answers?

We (in UK) have a commercial outfit - "Spotless" - selling RO water for cleaning windows. They are proud to announce their RO equipment has a 99% rejection rate. Makes for easy calculation of water treatment salt additions! But you would not want that water in your copper pipes! (Or to drink as-is). Pipes with any metal for that matter. Water with no alkalinity will eat them for breakfast! But most here seem equally proud their water has zero minerals? RO water for drinking is "remineralised", but we don't hear much about that. You can see it in the Bru'n Water calculator (I've seen the same "Profile" in other calculators too):

The mineral salts present must be the result of post-filter "remineralisation". No vendor of RO devices is going to admit their membranes allow 16ppm (bicarbonate) through.

Comments please ...

 

[day_trippr]

[shrug] My RO output consistently ranges between 9 and 11 ppm (input water is typically ~250ppm and quite hard). That's essentially "zero" in the big picture but I distributed 10 points across that Bru'n Water section at the same ratios as my raw water test results. Probably not "accurate", but again, probably doesn't matter, either...

Cheers!

 

[Buckeye_Hydro]

A second go at this 'cos I didn't gather any useful way forward from the first. Perhaps the resident RO Water guru (@Buckeye_Hydro) has my answers?

We (in UK) have a commercial outfit - "Spotless" - selling RO water for cleaning windows. They are proud to announce their RO equipment has a 99% rejection rate. Makes for easy calculation of water treatment salt additions! But you would not want that water in your copper pipes! (Or to drink as-is). Pipes with any metal for that matter. Water with no alkalinity will eat them for breakfast! But most here seem equally proud their water has zero minerals? RO water for drinking is "remineralised", but we don't hear much about that. You can see it in the Bru'n Water calculator (I've seen the same "Profile" in other calculators too):

View attachment 864123

The mineral salts present must be the result of post-filter "remineralisation". No vendor of RO devices is going to admit their membranes allow 16ppm (bicarbonate) through.

Comments please ...

Sorry, but its not clear to me what your question is!

 

[Peebee]

Sorry, but its not clear to me what your question is!

"Remineralisation filters". Please tell me about them ... or rather, please tell everyone about them 'cos I'm not about to get RO Water (in N. Wales, like in the Scottish Highlands, there isn't much in the water ... apart from the odd drowned sheep). I know RO Units can have them (post RO filter, especially whole-house units) to manage the otherwise acidic water, but I know little in the way of detail, and I suspect many don't.

I'm particularly interested in how they modify alkalinity but intrigued by what else they might do (as standard).

 

[Buckeye_Hydro]

The most common are simply calcite (calcium carbonate) - will add minerals as long as the pH is below 7.

There are many different remin cartridges on the market with all manner of components

 

[Punkjah007]

Buckeye - Is this an accurate profile for RO water?

 

[VikeMan]

Buckeye - Is this an accurate profile for RO water?

It's "accurate" in the sense that it's possible. But each RO sample will be different, depending on the water's profile before filtering and on the efficiency of the filter.

 

[Buckeye_Hydro]

Is your RO water 30 ppm TDS? Seems pretty high.

 

[DaveDiamond]

I noticed something similar yesterday. I bought a hydrometer online and it's useless so the seller wanted proof. I usually buy distilled water and my aquarium hydrometer shows that as being exactly 1.000. This time I happened to buy demineralised water, and that is showing 1.002/3. I assume that's due to minerals being left behind as you're showing here. So what you're experiencing might just be standard.

 

[VikeMan]

I noticed something similar yesterday. I bought a hydrometer online and it's useless so the seller wanted proof. I usually buy distilled water and my aquarium hydrometer shows that as being exactly 1.000. This time I happened to buy demineralised water, and that is showing 1.002/3. I assume that's due to minerals being left behind as you're showing here. So what you're experiencing might just be standard.

I don't know what's going on with your hydrometer or your water, but at the concentrations being discussed, the difference in gravity due to the remaining ions would be unmeasurable with a standard hydrometer. For example, water with 30 ppm TDS would have a gravity of approximately 1.00003.

 

[Peebee]

... water with 30 ppm TDS would have a gravity of approximately 1.00003

Thanks VikeMan! Or at the very least, thanks on behalf of everyone else here ... you've saved them from a long lecture on Pyknometers and four decimal places of a gram weighing scales. I don't do my reputation any good at all going on, and on, (yawn) about pyknometers. Don't know why. Oops, shouldn't have said that, someone's goin' to tell me now.


Anyway ... that "Defuddler" thing attached in my signature below has a RO Water "profiler" buried in it for those that have the source water profile (at least, the "development" version does). Or ... it has a stab at it: Lets you decide what the rejection rate is (%) but applies the same value to all relevant ions, which isn't quite correct, but hey, you've next to nothing anyway. Plus, in line with what this thread is about (I am the "OP") some RO Waters get a subtle "remineralization". (That's for other readers; if you're a "Grannie" I'm not teaching you how to suck eggs!).

 

[mabrungard]

30 ppm TDS is typical when your raw water source has 700 ppm TDS. I expect that some locations with much lower raw water TDS would show a lower RO TDS for that reason. The RO profile shown in Bru'n Water is an actual Ward Labs result.

 

[DaveDiamond]

I don't know what's going on with your hydrometer or your water, but at the concentrations being discussed, the difference in gravity due to the remaining ions would be unmeasurable with a standard hydrometer. For example, water with 30 ppm TDS would have a gravity of approximately 1.00003.

I see. I don't know why demineralised water shows 1.002 when distilled water shows 1.000, but it's not the hydrometer, else distilled wouldn't read 1.000 as it should. I didn't know the concentrations being discussed were that low, it sounds pretty irrelevant to me then.

 

[Peebee]

I see. I don't know why demineralised water shows 1.002 when distilled water shows 1.000, ...

Temperature perhaps? An SG of 1.002 is about the difference of water measured at room temperature and fridge temperature.

I didn't know the concentrations being discussed were that low,

I see you're Australian (from your profile). You haven't the excuse of the Americans ... you work with metric SI units, and "mg/L" (near identical to "ppm" in water) will put 30mg/L at 0.000003g in a litre. SG (a ratio, where water is always one 'cos the other half of the ratio is water) looks like mg/L, so 30mg/L has an SG around-about 1.00003. (Hope I counted the zeros right, me eyes go wonky looking at rows of the same thing!).

You know now!

 

[Peebee]

Crikey, why have I never seen this before ...

You've a suspect hydrometer (and you've lost your thermometer): No problem!

Take the "SG" of your wort. Let's say it's 1.056 on the dodgy hydrometer.

Take the "SG" of water (that has about the same temperature as the wort) with the same hydrometer ... let's say it's 1.002.

1.056/1.002 is SG1.054. Temperature compensated too!

And I haven't even mentioned "pykn.... (got him)

 

[IslandLizard]

you work with metric SI units, and "mg/L" (near identical to "ppm" in water) will put 30mg/L at 0.000003g in a litre.

My emphasis in bold/red ^
That should be 0.000030 for 30mg/L.

The last "0" in that is meant to show the (true) precision in relevant decimals.

 

[DaveDiamond]

Temperature perhaps? An SG of 1.002 is about the difference of water measured at room temperature and fridge temperature.


I see you're Australian (from your profile). You haven't the excuse of the Americans ... you work with metric SI units, and "mg/L" (near identical to "ppm" in water) will put 30mg/L at 0.000003g in a litre. SG (a ratio, where water is always one 'cos the other half of the ratio is water) looks like mg/L, so 30mg/L has an SG around-about 1.00003. (Hope I counted the zeros right, me eyes go wonky looking at rows of the same thing!).

You know now!

Temperature might have been a factor. I didn't check it on the hydrometer, but I'm guessing when I checked the distilled water it would have been room temperature, the demineralised water I had left outside on the porch and brought it in in the middle of the night. Not fridge cold, but definitely colder as we're getting 30c/86f days, but some crisp spring nights. I'll have to buy some distilled and check.
I think I've sidetracked this thread though!

 

[Peebee]

Yeah, temperature sounds like the culprit.

Try the trick with the hydrometer (measuring water at the same time ... as long as the water is about the same temperature as the beer, within a degree C say, and the scale isn't smudged and distorted), It really will work! It's what SG was for (hydrometers just borrow it). And you get temperature compensation for nothing. The "two points" difference compensation I quoted may be an underestimation - hydrometers have two compensations (one for sample, one for the water reference) not one and I was only quoting on the one (I can't use hydrometers 'cos of me wonky eyes ... I was quoting from what I know of pyknometers).


And you can cut the reminders it's getting warmer down your way! I get jealous 'cos it's getting colder up here ... yesterday's gale broke the top off the 50 foot tree in the garden. [EDIT:] Perhaps an advantage of having a small garden ... The top of me tree landed in next-door's garden

 

[MaxStout]

Thanks VikeMan! Or at the very least, thanks on behalf of everyone else here ... you've saved them from a long lecture on Pyknometers and four decimal places of a gram weighing scales. I don't do my reputation any good at all going on, and on, (yawn) about pyknometers. Don't know why. Oops, shouldn't have said that, someone's goin' to tell me now.


Anyway ... that "Defuddler" thing attached in my signature below has a RO Water "profiler" buried in it for those that have the source water profile (at least, the "development" version does). Or ... it has a stab at it: Lets you decide what the rejection rate is (%) but applies the same value to all relevant ions, which isn't quite correct, but hey, you've next to nothing anyway. Plus, in line with what this thread is about (I am the "OP") some RO Waters get a subtle "remineralization". (That's for other readers; if you're a "Grannie" I'm not teaching you how to suck eggs!).

More pyknometers!

CSB time: the AHA published an article on hydrometers in the July/August 2025 issue of Zymurgy. The article also included a chart of comparisons with refractometers and $400-$60,000 gravimetric density readers. I was so tempted to write in to ask why they didn't include some discussion of pyknometers, but good sense caught up with me...

Back OT with the discrepancy issue of distilled vs RO water. A $20 pyknometer and $20 gram scale (the latter of which many of us already have) would be a cheap and easy way to calibrate against a sample under test. I have three triple-scale hydrometers that I tested using the pyknometer I bought. One is spot-on, the other two are off a couple thousandths.