Getting a TDS meter

[Jag75]

When a TDS meter reads the ppm what does that ppm consist of. Is it all the stuff added up? What should RO water ppm be for best results?

 

[Qhrumphf]

When a TDS meter reads the ppm what does that ppm consist of. Is it all the stuff added up? What should RO water ppm be for best results?

Yes. Pretty much all the "stuff" added up.

From what I understand (and there are other regulars to this section who understand far better than I), the total left behind by RO filtration depends on the level in the source water. But unless your source water levels are stupidly high in "stuff" I'd expect RO water to have a TDS ppm below 10, or at least below 20. I think with a well working filter it's an order of 98 or 99% reduction, so even stupidly high source levels should come out negligible.

 

[Silver_Is_Money]

ppm TDS = ppm Ca + ppm Mg + ppm Na + ppm (sum of all other minor cations) + ppm Cl + ppm SO4 + ppm HCO3-/2 + ppm (sum of all other minor anions)

***For TDS, always remember to divide your ppm of HCO3- (the bicarbonate ion ppm) by 2.***

In my opinion "good" RO water reads 10 ppm TDS or below.

Ballpark 80% of RO waters ppm TDS will be its ~ppm measure of alkalinity. This rather loose ballpark association is valid only for RO water.

61/50*alkalinity = bicarbonate
50/61*bicarbonate = alkalinity

My well water reads ~876 ppm on my TDS meter, and my RO water reads ~45 ppm TDS, of which I presume ~36 ppm to be alkalinity, placing my bicarbonate at ~44 ppm.

45/876 = 0.05, or 5%, so for my unit (operating in the real world, not via theory) 95% of all extant cations and anions are being removed.

The better your source water TDS, the better will be your RO water TDS.

 

[Silver_Is_Money]

It turns out as an outcropping of my down and dirty, and admittedly not highly tested and verified, loose ballpark rule of thumb as seen above, you can make an even more loose first wild "assumption" (for RO water only) that:

ppm TDS ~= ppm of Bicarbonate ions (for only RO water)

This may land you a bit on the high side of your actual ppm bicarbonate, but it will likely be ballpark adequate for making adjustments to alkalinity if no other and better alkalinity/bicarb information on your RO water is available to you.

YMMV, and therefore I ask you to test this against your hard RO water data and report your findings, so the ballpark TDS to alkalinity as bicarbonate association can be made stronger through cumulative RO water TDS and alkalinity data correlation.

 

[Jag75]

Thanks guys . I dont have RO water at home . I use primo RO inside Walmart. I started looking into water profiles about 6 months ago . Sent my water to ward labs . So I've been using salts and acids to adjust my water and even diluting with RO water . I'm just trying to wrap my brain around ppm for RO water . When brewing with 100% Ro water does the ppm of the TDS meter determine how much acids or salts you add? Or is say 20ppm so low it doesnt matter .

 

[Silver_Is_Money]

Thanks guys . I dont have RO water at home . I use primo RO inside Walmart. I started looking into water profiles about 6 months ago . Sent my water to ward labs . So I've been using salts and acids to adjust my water and even diluting with RO water . I'm just trying to wrap my brain around ppm for RO water . When brewing with 100% Ro water does the ppm of the TDS meter determine how much acids or salts you add? Or is say 20ppm so low it doesnt matter .

Certainly 10 ppm TDS is so low it doesn't matter much. At 20 it may. I'm presently trying to see if indeed there is any correlation between TDS and alkalinity in another 'Brewing Science' thread.

 

[Jag75]

Silver at what ppm of RO water would you just say screw it and just use tap water ?

 

[Silver_Is_Money]

Silver at what ppm of RO water would you just say screw it and just use tap water ?

That would simultaneously depend upon the TDS of the tap water (and more preferably, a Ward Labs analytical report for the tap water). When it comes to tap water, the analyticals hold the key. Without them, accurate mineral adjustment isn't possible (even if alkalinity adjustment is as simple as mildly acidifying the tap water until one achieves a pH of ~5.4).

And then there is the chlorine/chloramines issue to contend with for tap water. And potentially iron and/or manganese...

 

[Jag75]

My water isnt too bad . I've diluted with RO water at times and sometimes use 100% Ro. I'm gonna do an IPA and am thinking of using all RO water and no tap. I get my RO water from a machine so I'm not sure what the water #'s going into the filters .

 

[Silver_Is_Money]

I would cut your tap water 50:50 with RO, to cut the 111 ppm of SO4 in half, as well as cut the 75 ppm Na in half.

To the 50:50 blend I would then add only some CaCl2 (to bring the calcium and chloride back up) and some Phosphoric Acid to hit pH 5.4 and thereby reduce the alkalinity (with complements to AJ for his "Zero Effective Alkalinity Method", as can be seen in a 'Brew Science' sticky).

AJ's 'Zero Effective Alkalinity Method' simultaneously solves any concerns as to the TDS/alkalinity of your RO water.

 

[Jag75]

Thanks Silver for your time

 

[RPh_Guy]

For TDS, always remember to divide your ppm of HCO3- (the bicarbonate ion ppm) by 2

Can you explain this please?

Why is actual bicarbonate ion concentration twice what the TDS meter is reporting?

 

[Silver_Is_Money]

Can you explain this please?

Why is actual bicarbonate ion concentration twice what the TDS meter is reporting?

The answers you seek are to be found here:
https://www.usbr.gov/lc/phoenix/programs/cass/pdf/Phase1/ATechapdxTDS.pdf

I quote:

The TDS of a water sample may also be estimated by summing the concentrations of the principal cations and anions. However, to accurately obtain, by summation, a result comparable to that determined by the evaporation method, only one-half of the HCO3 value is to be used since, under the evaporation method, carbon dioxide (CO2) and water of hydration (H2O) which make up approximately one-half of the HCO3 would be driven off and not included in the residue.

Plus read all about it in this thread (where AJ gets to the bottom of it):
https://www.homebrewtalk.com/forum/...-suitability-for-brewing.656765/#post-8414736

Interestingly enough, on the immediately above referenced page, Ward Labs TDS is once again 0.60 * uS/Cm.

 

[RPh_Guy]

OK so a TDS meter doesn't really report true TDS. That makes sense now, thanks.

 

[Jag75]

Huh ok so now I've read those links . Was getting a TDS meter a waste? I really cant hang with some of you guys when it comes to water science. You guys are like doctors, engineers or chemists....and I'm just a correctional officer lol

 

[RPh_Guy]

A TDS meter is great for checking RO water quality.
Under 10ppm you can basically ignore any dissolved ions.

 

[Silver_Is_Money]

Huh ok so now I've read those links . Was getting a TDS meter a waste? I really cant hang with some of you guys when it comes to water science. You guys are like doctors, engineers or chemists....and I'm just a correctional officer lol

A TDS meter is at best merely a ballpark device with respect to TDS. It is really a conductivity meter with a built in multiplicative factor that permits it to ballpark an 'ersatz' TDS (which for most purposes is likely to be good enough). Though if you know its built in multiplicative factor it should give a very good conductivity indication.

If you don't know your TDS meters built in multiplicative factor, 0.60 should be a reasonable first wild guess, in case you actually need to read conductivity when using it. I've seen several which specify 0.64. Hanna's generally specify 0.5.

I speculate that the multiplicative factor may come down to the specifics for the calibration salt, but then most budget TDS meters do not offer a calibration option. If the mix of salts and bicarbonate species within your sample water are a reasonably close match to those of the manufacturers chosen calibrant salt(s), you stand a better chance of getting a reliable TDS reading, but if not, then the reliability of the TDS output is more suspect.

 

[Jag75]

So when you take the ppm from a TDS of Ro water and you multiply it by .60?

I guess I really got the TDS to check the quality of the RO water I will be getting from primo dispenser.

 

[Silver_Is_Money]

So when you take the ppm from a TDS of Ro water and you multiply it by .60?

No, you accept it at face value as TDS, with the knowledge that it is merely ballparking (or estimating) the TDS.

If you want to know your waters conductivity in units of MicroSiemens (or units of: uS/Cm) divide TDS by something in the neighborhood of 0.60 as a first guess, or by the units actual internal multiplicative factor if you know it.

The next level is to try to determine alkalinity (or bicarbonate) from merely a TDS meter reading of RO water. That is for my other thread though.

The utility in this is that TDS meters have come down to the price range of only about $7.

 

[Jag75]

Thanks all . I appreciate the time you guys offered to help me try and understand this.

Under 10ppm it's great
TDS is just a ballpark estimate .
Got it ty !

 

[Silver_Is_Money]

I've just scanned several additional Ward Labs water reports on HBT, and in each case I've come across the reported Ward Labs TDS reading is very close to 0.60 x conductivity in uS/Cm (within permissible rounding error).

They actually report conductivity in units of micro-mhos, or mmhos (wherein a mho of conductivity is the reciprocal of an ohm of resistance). Multiply mmhos by 1,000 to convert them to MicroSiemens (or uS/Cm).

For example, if Ward Labs reports conductivity of 0.46 mmhos:

0.46 x 1,000 = 460 uS/Cm

460 uS/Cm x 0.60 = 276 ppm TDS

Confidence is (for me at least) growing that they simply take a mmhos unit conductivity reading of your water sample and then multiply it by 600, whereby the result becomes their reported TDS. I have doubt as to their doing an actual evaporation to ascertain a more realistic TDS. And they do not appear to be using the TDS via ion summation method (with HCO3- being divided by 2) either.

This information and $3.50 might get you a nice cup of coffee at Starbucks.

 

[Jag75]

Silver your right ! I just looked back at mine and did the equation. Mine came out to 342 . My report said 345 . I think I'm starting to grasp this lol

 

[RPh_Guy]

This information and $3.50 might get you a nice cup of coffee at Starbucks.

LOL!!

 

[Jag75]

LOL!!

It was pretty funny wasn't it

 

[IBRUTOO]

So at what level is an acceptable TDS for using as brew water without RO? I have well water that reads 90 on the TDS meter.

To go a step further can you get an estimate of the different ion concentrations from other available tests from most pool water test kits? Did a hardness check and reads about 95ppm (pool test kit think it is calcium hardness) and total alkalinity of 60ppm.

 

[day_trippr]

fwiw, as long as the iron is below .3 ppm any well running at TDS 90 is almost certainly going to be fine for brewing...

Cheers!

 

[Silver_Is_Money]

So at what level is an acceptable TDS for using as brew water without RO? I have well water that reads 90 on the TDS meter.

To go a step further can you get an estimate of the different ion concentrations from other available tests from most pool water test kits? Did a hardness check and reads about 95ppm (pool test kit think it is calcium hardness) and total alkalinity of 60ppm.

TH = 2.5(Ca++) + 4.12(Mg++)
(where TH = total Hardness in ppm = GH*17.848)

So if your GH derived total hardness is 95 ppm, lets take a wild guess that ballpark 80% of that hardness is from calcium, and ballpark 20% is from magnesium.

95 x 0.80 = 76
95 x 0.20 = 19

76 = 2.5(Ca++)
Ca++ = 30.4 ppm

19 = 4.12(Mg++)
Mg++ = 4.6 ppm

There, now we have ballpark ppm's for your calcium and magnesium mineralization as derived from your GH fish tank hardness kit alone. But since we took the liberty above to split the TH equation into two parts, let's reassemble it and double check:

TH = 2.5(30.4) + 4.12(4.6) [the whole equation, now back together again]
TH = 76 + ~19
TH = 95

Since we got back to 95 ppm of total hardness, it worked perfectly provided that a very small allowance is made for my earlier Mg++ ppm rounding error.

So now we know that your TDS is 90, your KH fish tank kit derived alkalinity is 60 (which means your bicarb is 61/50 x 60 = 73.2 ppm), your calcium is somewhere near 30.4 ppm, and your magnesium is somewhere near 4.6 ppm.

90 ppm TDS = 30.4 + 4.6 + Na + Cl + SO4 + (73.2)/2
Na + Cl + SO4 = 18.4 ppm

That's about as far as I believe I can take this via such numerical game playing.

 

[Jag75]

So your saying you can take a TDS reading and determine hardness, alkalinity, sodium ect.....?

 

[Silver_Is_Money]

So your saying you can take a TDS reading and determine hardness, alkalinity, sodium ect.....?

No, but you can take a GH/KH fish tank water test kit (about $9) and do a lot with it, and the TDS meter can assist.

 

[Silver_Is_Money]

90 ppm TDS = 30.4 + 4.6 + Na + Cl + SO4 + (73.2)/2
Na + Cl + SO4 = 18.4 ppm

That's about as far as I believe I can take this via such numerical game playing.

"But that was yesterday, and yesterday's gone." (from a song by Chad & Jeremy, I'm aging myself here)

Today I desire to go somewhat further. The tool that permits this is any program (such as Brun' Water, or Mash Made Easy, or others) which permits one to perform cation/anion balancing on a mEq/L to mEq/L basis.

But therein lies the dilemma. One or more of the givens can not be correct on the basis of mEq/L cation and anion balance. The "given" suspects are:

1) GH (general, or total hardness) [from whence is derived ppm total hardness)
2) KH (carbonate hardness, or alkalinity) [from whence is derived ppm alkalinity and then ppm bicarb]
3) TDS
4) The wild guess presumption of 80%/20% of hardness attributable to calcium and magnesium respectively.

The cation mEq/L value is too great to be balanced by any combination of merely 18.4 ppm of strictly anions Cl- and SO4-- (even for the case where Na+ is set to zero), and knowing the nature of TDS via meter to be highly suspect as to accuracy, I suspect a good portion of the problem lies with #3. If (for example) TDS was to be 96 ppm or a bit greater, rather than accepting it as the meter indicated 90 ppm, then cation/anion balance can be achieved.

Any mix of percentages chosen for Ca++ and Mg++ hardly moves the cation mEq/L scale at all, so #4 can be eliminated.

if KH was a bit higher, and therefore alkalinity was a tad higher, this also works to the favor of achieving cation/anion mEq/L balance.

The first 3 in general can all be considered suspect. The 4th is merely a derivative of the 1st, and thereby can now be discounted via two means. But I do suspect that TDS is highly likely off, and that "perhaps" KH is off. Both slightly to the low side.

It can merely be speculated, but I will presume that sodium (Na+) is very low, and that the sum total of Cl- and SO4-- ions is on the order of (at a minimum) ballpark 26 ppm (or a bit higher if Na+ is not zero), rather than 18.4 ppm. I also suspect that ppm Cl- is likely to be greater than ppm SO4--.