Latest analysis, on coffee brewing relevant things, of my well water, all mg/L:

Ca 68.2
Mg 6.33
So 22
Alkalinity (CaCO3) 180
Hardness 200
TDS 280
pH 7.3


Will diluting it with distilled water cut all those measurement to the percentage of water that is well water?


For example, if I used 25% well 75% distilled, would it cut all those measurements, except pH, to ~1/4 of the 100% well water amounts per liter? Or would some of those measurements not dilute proportionately like that - if so, which would not?

Ca 17
Mg 1.6
So 5.5
Alkalinity 45
Hardness 50
TDS 70

Acavia wrote:For example, if I used 25% well 75% distilled, would it cut all those measurements, except pH, to ~1/4 of the 100% well water amounts per liter? Or would some of those measurements not dilute proportionately like that - if so, which would not?

Ca 17
Mg 1.6
So 5.5
Alkalinity 45
Hardness 50
TDS 70

Yes, although the TDS as measured by a typical conductivity meter might not be exactly 70 (conductivity can be nonlinear with the dissolved ion concentration).

Thanks. I have some Wendelboe coffee, and that would hit close to the profile for Oslo water, which is high in calcium versus magnesium.

homeburrero wrote:Yes, although the TDS as measured by a typical conductivity meter might not be exactly 70 (conductivity can be nonlinear with the dissolved ion concentration).

Would TDS being in the ball park of the proportions or would it tend to fall more or less?

It would be in the ballpark, and for some ions, like NaCl or KHCO3 it would be pretty exact. But some ion dilutions, MgSO4, for example, would tend to read a little higher than your calculated value. For example if you were to read 200 mg/L of MgSO4 with an inexpensive TDS meter with a 0.5 calibration factor it would indicate about 165 ppm. If you diluted that with 75% distilled you would expect to read about 41 ppm, but it would read closer 49 ppm.* Considering the inaccuracies inherent in using conductivity to estimate TDS, including temperature dependence, being in the ballpark is all you can expect.


* This example calc is based on conductivity calculations using a handy online calculator: http://www.aqion.onl/show_ph

P.S. You sometimes see a reference to a "4-4-2" calibrated TDS meter, especially in reference to the old SCAA recommendation of 150 ppm as the ideal. The meter used by the SCAA used a different calibration solution that is supposedly more like "natural water", and when calibrated for accuracy in the 150 ppm range use a calibration factor of 0.65 ppm per µS/cm. Almost all of the inexpensive meters in popular use now are calibrated against NaCl and use a conversion factor of 0.5 ppm per µS/cm. So if you are using one of these NaCl calibrated meters and for some reason want to hit the exact conductivity as recommended by that old SCAA spec, your ideal reading would be in the neighborhood of 115 ppm rather than 150. In reality there is a wide variety in the mineral makeup of natural water, and it's best not to focus too much on hitting any prescribed TDS reading.

My reported numbers were from a laboratory based on water samples. So a snapshot at that time how ever they measured it.

Acavia wrote:I have some Wendelboe coffee, and that would hit close to the profile for Oslo water, which is high in calcium versus magnesium.

Yes, that dilution should do a good job of that. I recently found and posted some Oslo water numbers here: Oslo water.