A method for measuring the Alkalinity of your RO water

[Silver_Is_Money]

Alkalinity kits can make it nigh on impossible to accurately determine the Alkalinity [as CaCO3 in mg/L (ppm)] of RO water. This is an alternative method:

RO Water alternative Alkalinity determination:

Givens:

1 drop from a standard 'old style' medicine type eye dropper (generally these are glass tubes with a rubber squeeze bulb) ~= 0.10 mL (presumed, or you can compute this for greater precision)

For purely trivial reference: 1 single eye dropper drop of 10% Phosphoric Acid (presuming that it is 0.10 mL) should drop 10L of fresh pH 7.00 deionized (DI) water to a pH of 4.96

For actual reference: 1 drop of 10% Phosphoric Acid removes 0.107885 mEq's of Alkalinity to "specifically" a pH of 4.96.

For actual reference: 1 mEq of Alkalinity (as CaCO3) = 50.04345 mg of CaCO3 by weight

Therefore, on to the Alkalinity test:

1) Add 1 eye dropper drop of 10% Phosphoric Acid to 10L of your RO water, mix well, and measure its pH at 20 degrees C.

2) Continue adding eye dropper drops one at a time, mixing well, and measuring the RO waters pH at 20 degrees C. until the RO water finally hits or goes below a measured pH of 4.96. Carefully count how many drops of 10% Phosphoric Acid this took.

3) Multiply the total number of eye dropper drops x 0.107885. Record your answer as "mEq's_acid".

4) Alkalinity mg/L (~ppm) computation:

mEq's_acid x 50.04345 = "mg of CaCO3" present within your test volume of RO water.

Answer = "mg of CaCO3"/Liters = mg/10L = mg/L Alkalinity ~= ppm Alkalinity

Reference Hint: 15 eye dropper drops of 10% Phosphoric Acid into 10 Liters of RO to reach 4.96 pH = ~8.1 mg/L (ppm) Alkalinity, or 30 drops = ~16.2 mg/L (ppm) Alkalinity

 

[Vale71]

Why would you want to measure RO water's alkalinity at all? If the system is working properly it will be in the 1-5 ppm range at most which has basically no effect on mash chemistry. Besides that fresh RO water has a PH that is anything but 7 so you'd have to consider the starting point as well. If you wait long enough RO water will then become acidic by itself because of CO2 absorption from the atmosphere making it basically impossible to do what you propose.

 

[Big Monk]

Why would you want to measure RO water's alkalinity at all? If the system is working properly it will be in the 1-5 ppm range at most which has basically no effect on mash chemistry. Besides that fresh RO water has a PH that is anything but 7 so you'd have to consider the starting point as well. If you wait long enough RO water will then become acidic by itself because of CO2 absorption from the atmosphere making it basically impossible to do what you propose.

I have to agree here. If you really need to input this into your calculator, measure RO/DI water pH directly and assume ~1.58 ppm Alkalinity as CaCO3, which if i'm not mistaken is what A.J. always proposed as the standard (an actual laboratory standard, the source of which escapes me at this point).

It does not hurt to account for this but the difference is, in all practical sense, completely negligible.

 

[Silver_Is_Money]

Granted, for most of us this will not matter much, but the exercise offers education intended for learning purposes none the less.

In my case, my well water has both extremely high Total Hardness and Alkalinity. My TDS meter reads ~856 ppm on water from the well, and also from my standard sink taps, post our water softener. My uS/cm conductivity meter reads ~1,290 on the well water. The local water softener supplier and servicer guy's TDS meter had it at ~910 ppm. From attempting to use a fish water alkalinity test kit on the water coming from my homes under the sink RO unit, I suspect that my RO waters alkalinity is potentially in the ballpark order of 25 to 50 mg/L, but observing the color change is nigh-on impossible.

Historically, I've only used my well water once to brew beer, at a volume ratio of 1 part well to 3 parts RO. The beer actually came out fine, but as I recall the water blend required a lot of 88% Lactic Acid to get it to ~pH 5.6. I've never used any portion of the well water for brewing after that.

 

[Vale71]

I suspect that my RO waters alkalinity is potentially in the ballpark order of 25 to 50 mg/L, but observing the color change is nigh-on impossible.

If that is indeed the case then your RO unit is desperately in need of serious maintenance. That is, if you want it to actually output RO water...

 

[Silver_Is_Money]

I forgot to add that post the RO unit our waters TDS reads 46 mg/L using the same TDS meter which indicates 856 mg/L from the well water.

46/856 x 100 = 5.37% of the original TDS.

My RO waters alkalinity could easily be in the vicinity of 25 - 35 mg/L since the formula for TDS only counts ~half of extant Bicarbonate. As to why this is so, see this linked thread titled "Please advise on my tap water suitability for brewing", starting at post #11 and culminating at post #31.
Please advise on my tap water suitability for brewing.

 

[Silver_Is_Money]

20 ppm sodium (Na+) and 43 ppm alkalinity = ~46 ppm as TDS, because:
For 20 ppm sodium as the cation, in order for there to be cation/anion balance alkalinity must be 43 ppm. Therefore:

Bicarb = 43 ppm alkalinity x 61.01684/50.04345 = 52.43 ppm
TDS = 20 ppm Na + 52.43/2 ppm Bicarb. (halving the bicarb as required)
TDS = 46.21 ppm

So if my well water passes through a softener followed by my RO unit (such as it does), and the softener plus RO cleans house on everything and leaves behind only Na+ on the cation side and HCO3- on the anion side (such as can be speculated), and it reads 46 ppm TDS post the RO unit via my handheld meter (such as it does), my RO waters alkalinity (as CaCO3) has a maximum potential to be as high as 43 ppm.

EDIT: To the extent that some Cl- and SO4- survive the softener unit on the anion side of things, as is likely since softeners do not reduce these two ions, and the RO unit subsequently will not 100% reduce them (such as it won't), the actual alkalinity ppm will be somewhat lower than the absolute maximum calculated potential of 43 ppm. But not seemingly likely by an overwhelmingly appreciable percentage.

 

[Yooper]

I use a cheap aquarium kit, which measures gH and kH. One drop changing the color means that the alkalinity is 17 ppm or less, which is good enough for me. It doesn't matter to me if it's 2 or 15 ppm for my purposes.

 

[Bigdaddyale]

I use a cheap aquarium kit, which measures gH and kH. One drop changing the color means that the alkalinity is 17 ppm or less, which is good enough for me. It doesn't matter to me if it's 2 or 15 ppm for my purposes.

More information, please. Can you walk me through the process?