Reverse osmosis and Rpavlis water

Water analysis, treatment, and mineral recipes for optimum taste and equipment health.
MichaelR86
Posts: 2
Joined: 4 years ago

#1: Post by MichaelR86 »

Dear coffee enthusiasts,

Yet another long time lurker, but first time poster here. I recently decided to up my espresso game and bought a Lelit Bianca. I am currently using bottled water and a Lelit water softening filter since I live in an area with very hard water (around °20-23 dH). However, I would prefer to avoid the solution with bottled water and Lelit filters if possible, so I have bought a small table-top RO-system for the purpose of mixing my own water. During the past month, I've been reading and re-reading many of the very informative threads on water here on HB and I've taken the course on water at BaristaHustle. However, I am still not feeling entirely confident with the details and therefore, I would greatly appreaciate it, if you guys could help check/confirm my set-up.

My goal is to find a recipe that is fairly easy to make but is good for machine health (no corrision and minimal/zero scaling). I am willing to sacrifice a little bit on taste to prioritize machine health.
I want to start simple and use the famous Rpavlis water recipe, but using baking soda instead of potassium bicarbonate because baking soda is easier for me to acquire (I've also bought potassium bicarbonate and Epsom salt for later experiments).

I've tried to divide my post into three questions:

1) My RO water The tap-water in my area is generally considered to be safe, odor and taste free, but quite hard (20-23 dH). I have measured the TDS to 386ppm using a cheap TDS meter (TDS-3). I've also tested the output of my RO system and it always reads between 15 and 25 ppm. Most water recipies are based on distilled water, so I am wondering if my RO water is sufficiently 'pure' for coffee purposes? Is there anything I should be worried about in those 25ppm other than realizing that the online recipes might have to be slighly adjusted? I have read somewhere that one should be careful with recipies containing epsom salt (Magnesium Sulphate) if the water is not sufficiently pure because of potential scaling issues.

2) Mixing Rpavlis water I made a bottle of "alkalinity-concentrate" using 10g baking soda and 1000g RO water. As a first attemt I mixed 8.4g of the concentrate with my 991.6g of RO water.
Testing the resulting water yielded the following measurements:

TDS: 61ppm
pH: 6.7 (measured using a cheap pH meter)
Alkalinity: 60ppm as CaCO3 eq. (measured using the Red Sea Reef Foundation Pro kit)

Since the alkalinity is higher than the desired 50ppm CaCO3 eq., I assumed that the RO water contained a small amout of bicarbonates. Therefore, I adjusted the recipe to 7g of concentration and 993g of RO water, which gave the following results:

TDS: 54ppm
pH: 6.9
Alkalinity: 50ppm as CaCO3 eq.

Does this look reasonable to you guys or is there anything elso I should be aware of?

3) Corrision and scaling I've read many times that the Rpavlis water should be both corrision-safe and not cause any scaling at all. Several people who seems to be very knowledgable on water chemestry have stated this, so I trust this. However, when I enter the above measurements into the WaterGeek app, it tells me that the resulting Langerier index @ 95 degrees Celsius is -1.81, which can lead to corrision of metals. The app also requried me to specify the hardness of the water. I do have a titration-kit for measuring Calcium and magnisium content, the amounts seem to be so small that they can't be detected with my test kit (or my lab skills are not sufficiently good). For this reason I set the hardness to 0.1 dH (smallest possible value allowed in the app). Can anyone explain this? What am I missing?

Any tips and advice are greatly appreciated. Thank you very much.

Best regards,
Michael

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homeburrero
Team HB
Posts: 4863
Joined: 13 years ago

#2: Post by homeburrero »

MichaelR86 wrote:I've also tested the output of my RO system and it always reads between 15 and 25 ppm. Most water recipies are based on distilled water, so I am wondering if my RO water is sufficiently 'pure' for coffee purposes? Is there anything I should be worried about in those 25ppm other than realizing that the online recipes might have to be slighly adjusted? I have read somewhere that one should be careful with recipies containing epsom salt (Magnesium Sulphate) if the water is not sufficiently pure because of potential scaling issues.
No need to worry here, even if that ~20ppm coming thru the RO is calcium carbonate it's not gonna scale, nor drop calcium sulfate deposits even if you were to add some magnesium sulfate. (But if you have anything in there other than sodium or potassium bicarbonate, you should always take care to not over-concentrate your steam boiler water. If you do frequent steaming, then do periodic flushing out the hot water tap.)

MichaelR86 wrote:Does this look reasonable to you guys or is there anything elso I should be aware of?
Looks reasonable. 60 ppm on a TDS-3 (NaCl conversion factor) meter is about right for your mix. I don''t think you need to shift down to hit that 50 mg/L alkalinity measure, but is OK to do since you may be starting with a little alkalinity in the RO water.


MichaelR86 wrote:However, when I enter the above measurements into the WaterGeek app, it tells me that the resulting Langerier index @ 95 degrees Celsius is -1.81, which can lead to corrision of metals. The app also requried me to specify the hardness of the water. I do have a titration-kit for measuring Calcium and magnisium content, the amounts seem to be so small that they can't be detected with my test kit (or my lab skills are not sufficiently good). For this reason I set the hardness to 0.1 dH (smallest possible value allowed in the app). Can anyone explain this? What am I missing?
LSI calculations, and the apps that rely on them are not useful when evaluating these unnatural water recipes that contain little or no calcium. The LSI and the Puckorius are predicated on calcium hardness, so when you use total hardness in the equation and use a home-made water that is most or all magnesium the scale calculation will be off. And even if you use calcium hardness to calculate your LSI, a high LSI may be a pretty good scale indicator, but a low LSI is not necessarily an indicator of corrosivity. I haven't tried the Water Geek android app, but even the popular La Marzocco water calculator is simplistic, and pretty useless with home water recipes. One tool that I do sometimes find useful with these recipes is the aqion online calculator. Another is Marco Wellinger's spreadsheet: Mixing three waters.
Pat
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MichaelR86 (original poster)
Posts: 2
Joined: 4 years ago

#3: Post by MichaelR86 (original poster) »

Thank you for the very fast and detailed response. It is greatly appreciated :-)