I installed a nice water filtration system with cataylic carbon, reverse osmosis, and deionization.

I bought a $15 TDS reader from amazon. My unfiltered tap water has TDS of 398 ppm, and my filtered tap water has a TDS of 0. (Incidentally, the RO only gets it down to 80ppm TDS, and the DI takes it all the way down to 0).

Last year I bought the water test from Ward labs, and I just bought another one to test my water.

However, if a TDS reader shows 0 ppm, does that imply:

  • 0 ppm Sodium
  • 0 ppm Potassium
  • 0 ppm Calcium
  • 0 ppm Magnesium
  • 0 ppm CaCO3 (total hardness)
  • 0 ppm Chloride
  • 0 ppm Sulfate

I'm curious if I even need to do a test from Ward Labs given my TDS reader is 0 ppm.

3 Answers 3


In principle that's what it means. So you could stop there and use your water as if it were distilled water.

If you wanted to be thorough, you'd question the sensitivity of a $15 device.

A quick test is to take a quantity of your tap water and progressively dilute it with the 0ppm water, diluting your test sample in half each time (throw half away and top up with 0ppm water). You should see the TDS also half each time. Watch closely as the figure approaches 0pmm - you expect the series to reduce by half each time - any sudden jumps towards zero implies a lack of precision around that point.

And finally to be totally sure, you could try starting with distilled water, adding a known weight of salt and computing the expected TDS and compare that with the actual, and continually dilute the sample.

  • Hey MDMA, good idea; I'll try that. However, if we assume my $15 TDS reader passes this test, then is the answer to my question a yes? Commented Oct 26, 2015 at 17:39

According to the World Health Organization, Total Dissolved Solids constitutes:

'[T]he inorganic salts and small amounts of organic matter present in solution in water. The principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate, chloride, sulfate, and nitrate anions.'

According to the same report, when measuring TDS by conductivity (which is almost definitely what your meter is using) the 'quantitation limit for TDS in water [...] is 10 mg/litre'.

So, as long as your TDS meter is reliable and calibrated, while any of the particular brewing ions may not actually be exactly 0 ppm, you should at least be able to assume with confidence that it's a fairly insignificant amount.


Total dissolved solids in drinking water confer desirable taste and provide important, desirable, minerals to those drinking this water. Minerals generally include calcium, magnesium, potassium, and sodium compounds - often carbonates, bicarbonates, sulfates, and chlorides - all desirable substances. These are dissolved solids and a zero reading on a meter means that these important substances are absent.

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