Hi Folks, I recently got my espresso machine and decided to use Espresso Afficionado's TWW Espresso Inspired Water formula. I have been mixing 1.5g of Epsom salt and 0.5g of potassium bicarbonate into 1 gallon of distilled water per the instructions. I recently checked the TDS of this recipe using TWW's TDS machine, and the results are around 235. This seems very high, much higher than I was anticipating. For reference with the TDS meter, distilled water registers as 0, my tap is around 160, and filtered water from my fridge is about 140. Any idea why TDS of that water recipe is so high? Furthermore, do I need to be cautious with that formula given my machine has a brass boiler? Thanks all!

It looks like you may be using a 10 liter recipe instead of a 1 gallon recipe. Sorry, my bad, I answered your post in a hurry as my Wife was asking me some insurance related questions, so it looks like you have the dose right. Does your TDS meter use different reference settings?

Thanks for the reply! That's the holy water recipe. The one I'm following is a bit lower on the page:

Does your TDS meter use different reference settings?

I'm not entirely sure what you mean by this. Here is the TDS meter I'm using.

yakster wrote:Does your TDS meter use different reference settings?

Jbart1 wrote:I'm not entirely sure what you mean by this. Here is the TDS meter I'm using.

I think yakster was inquiring about what calibration factor your meter uses to convert its conductivity measure to TDS. Yours is a typical inexpensive TDS meter, which uses a factor of 0.5 typically calibrated on NaCl. This meter should give you a reading of about 150 ppm when used on actual TWW water. (Some TDS meters allow use of different calibration settings, and those calibrated to "4-4-2" solutions use a calibration factor close to 0.7, thus giving you a higher PPM value at the same conductivity.)

You can't expect to closely match the expected TWW reading, partly because your "TWW inspired" recipe is quite a bit different from actual TWW. It has a lot more potassium bicarbonate but lacks the calcium citrate that TWW uses. I would expect that your recipe (1.60 mmol/L MgSO4 + 1.35 mmol/L KHCO3) measured at 25 ℃, would have a conductivity in the ballpark of 465 µS/cm which would read about 233 ppm on a typical NaCl calibrated TDS meter.

(Here's the handy online calculator that I used to come up with my conductivity estimate: http://www.aqion.onl/show_ph)

TDS conductivity meters read electrical conductivity in micro Siemens per centimeter and a conversion factor is used to convert this conductivity into TDS based on the type of water being measured. The three common conversion factors are 442, NaCl, and KCl, but your meter has a fixed conversion factor so you can't change it. This chart shows that a conductivity reading of 1000 uS/cm converts to 500 ppm using the NaCl conversion factor and 700 ppm using the 442 conversion factor. I have an HM Digital COM-100 TDS meter and wasn't sure what conversion factor to use, since they give different readings so I was wondering if you were reading high based on your conversion factor, but it is odd that your water mixture is reading higher than your tap water.

As already pointed out, the OP's meter measures conductivity and who knows how it is calibrated. In any case, the manufacturer says the following about the "TDS" meter: NOTE: this will not define which minerals are present in your water, only that something is there.

Furthermore, the classic method to calculate of water "hardness" was to assess the risk of limescale build-up in boilers, so it was worked out to provide a good estimate of the concentration of the two commonest divalent cations (mainly Ca but also Mg) responsible for limescale formation in most water. There are other ions, like Fe and Mn that can also contribute to "hardness," but they are less common.

A conductivity meter is going to measure ALL ionized species dissolved in water and read out in some number of conductivity units (there are several).

This TWW water formula contains a lot of cations that are not Ca++. The only cation in the formula is Mg++ in epsom salts (Mg sulfate), which is less of a risk for limescale than Ca++, though I think the presence of carbonate anions (derivable from Na bicarb) increases the risk slightly. The other cations are K+ and Na+ which do not form scale.

Wow thanks for all the replies. Very much appreciate the input. So then would it be advisable to reduce the quantity of epsom salt/potassium bicarb? I'm thinking of switching to the holy water recipe. If my calculations are correct, this should change my conductivity to around 311 µS/cm, equating to about 150ppm on my TDS.

But it sounds like shooting for 150 is moot if epsom salt/potassium bicarb won't form scale? Would you folks recommend I tweak the recipe or possibly find another one altogether? I'm happy to adjust the formula to prevent having to descale and keep the machine happy

The OP is using the inexpensive TWW conductivity meter. TWW does not say, but I'm confident that their two-button TDS meter, like all similar inexpensive meters I've come across (Zerowater, iSpring , HM digital TDS-2 and TDS Easy, etc.) uses the simple NaCl calibration factor of 0.5. This is corroborated by this current post (where the OP was reading 235 ppm on a solution that should have a conductivity of 465 µS/cm) as well as previous posts. Here's a recent example where a user was using a 442 calibrated Com-100 meter and getting unexpected high ppm readings on his TWW water, then after switching to NaCl mode it came out right : Noobie Question: How To Treat Water (Water Report) .

Note: It may seem odd that the TWW folks targeted their water to read 150 ppm on an NaCl calibrated meter when the legacy SCAA standard that specified 150 ppm as an ideal was based on measurements with a 442 calibrated meter. You might think they would have chosen a recipe that reads 150 ppm on a 442 meter, and which would read only 115 ppm on an NaCl calibrated meter. But I think their choice makes sense because most everyone thinks that 150 ppm is the best number, and by far most all of them have a NaCl calibrated meter, and trying to explain the difference in simple terms can be messy and confusing.

Jbart1 wrote:So then would it be advisable to reduce the quantity of epsom salt/potassium bicarb? I'm thinking of switching to the holy water recipe. If my calculations are correct, this should change my conductivity to around 311 µS/cm, equating to about 150ppm on my TDS.

But it sounds like shooting for 150 is moot if epsom salt/potassium bicarb won't form scale? Would you folks recommend I tweak the recipe or possibly find another one altogether? I'm happy to adjust the formula to prevent having to descale and keep the machine happy

Shooting for 150 TDS is folly, especially when you have control of the calcium, magnesium, and bicarbonate.

You could try rpavlis, which would be 1.0 g potassium bicarb in 10 liters, and the half strength rpavlis which would be 0.5 g potassium bicarb in 10 liters and no Epsom salt. Either has reasonable alkalinity for corrosion protection, but go with the higher amount unless the other tastes better to you. Then you might experiment with adding in some Epsom at .5 g in 10 liters and 1.5 g in 10 liters. Neither would cause scale but if you can't taste an improvement go with the option that uses the least Epsom.