Hi,
Are there any preferred TDS meters in this forum? I'd like something that is accurate, affordable and will last. I am interested in beginning to experiment with different water recipes for both espresso and non-espresso.

Thanks & Peace.

Guess they are all basically the same? $15-$20 on Amazon should suffice?

Thanks & Peace.

They all work on the same principle, which is they measure the conductivity of the water.

One thing to keep in mind - is that they are only calibrated at a standard temperature of about 77f or 25c. Although the one I have is purportedly temperature compensated, it really doesn't seem to be.

Something cheap and simple would be my recommendation, and adjust your sample temperature when taking readings.

nuketopia wrote:Something cheap and simple would be my recommendation, and adjust your sample temperature when taking readings.

+1

They aren't all the same, but all of them measure conductivity and none of them give you an accurate measure of TDS, because different electrolytes have different factors for converting conductivity to ppm, and the accuracy depends on choosing the right conversion factor for your particular water. For natural freshwater, a 4-4-2* calibration is supposedly better at estimating PPM, but not always. To my mind the best bet is a cheap NaCl calibrated meter, which uses a conversion factor of 0.5 (i.e., PPM = conductivity microSiemen/cm X 0.5). Then if you measure your water at 25C, you can just double your PPM number to get the conductivity, then if you want a more accurate TDS multiply that by any conversion factor that is appropriate to your particular water.

(Or you can just use the ppm that it gives you, and not worry much about the fact that it could be pretty far off. In most cases, including coffee brewing water, an accurate TDS number is not all that important.)

Although a conversion factor of about 0.65 is considered appropriate for most low-moderate TDS tap water, that's not always the case. For example if you get your water from the Tolt river source in North Seattle, a factor of 0.5 would be more appropriate.

One common use of a TDS meter where the conversion factor of 0.5 is appropriate is in measuring the mineral increase from a calcite filter. If you measure the water before and after a calcite filter with an inexpensive NaCl calibrated TDS meter, the PPM increase shown on the meter will be close to the increase in calcium carbonate hardness (expressed as CaCO3.)

For comparing against the old SCAA ideal coffee water standard of 150 ppm TDS, you may need to adjust the number. That measure was supposedly done on a meter with a 4-4-2 calibration. If so, that would have been a conductivity of about 215-235 microSiemens/cm, which would read about 105-120 ppm using the NaCl factor of most modern inexpensive meters.

Some higher end TDS meters let you switch between NaCl or 4-4-2 calibration factors and some let you set them for any factor you want. The popular HM digital TDS meters use NaCl with a factor 0f 0.5 for all the inexpensive models. The COM-100, about 60 bucks, is their most inexpensive model that allows setting to either NaCl or 4-4-2.**

*4-4-2 is a calibration solution containing 40% sodium sulfate, 40% sodium bicarbonate, 20% sodium chloride developed by the Myron L company. It provides a slightly non-linear conversion factor that better approximates natural freshwater over a wide range (drinking water to irrigation water). At 150 ppm the conversion factor is about 0.65. More info here: http://www.myronl.com/PDF/application_b ... ssb_ab.pdf.

** Edit addition: The newer COM-80 meters also allow you to select either 0.5(NaCl) or 0.7(442) as a conversion factor for the PPM display, even though the current (2016) online manual still says that they only do ppm or ppt with a 0.5 or 500 (NaCl) factor.

COM-100. I find the cheap little pen ones don't tend to reflect reality nearly as well and aren't good for anything but "really soft, medium, really hard" as a whole unless you're extremely lucky with your unit. The COM-100 isn't perfect because it's still a conductivity meter, but at least it gets the conductivity right.

I have mentioned this before but I took my water to the pool guy in town and he gave me a full analysis for free. You could always try that.

Also, don't most municipal water supplies change their chemical mix with the temperature? That would mean you need to test each season.

homeburrero wrote: The COM-100, about 60 bucks, is their most inexpensive model that allows setting to either NaCl or 4-4-2.

the COM-80 is the same meter for approximately half the price, major differences are button batteries in place of the AAA and it's not water proof.

I've also used Oakton meters and find that they hold calibration better. They also have a selectable conversion factor.

CwD wrote:COM-100. I find the cheap little pen ones don't tend to reflect reality nearly as well and aren't good for anything but "really soft, medium, really hard" as a whole unless you're extremely lucky with your unit. The COM-100 isn't perfect because it's still a conductivity meter, but at least it gets the conductivity right.

+1. The AAA batteries make a difference. I've had issues with all the ones that use the circle batteries. I also like it because the SCAA TDS preferred is 150 using the 4-4-2. The cheapies don't have this mode usually.