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In response to our item about the commercial TDS (total dissolved solids) water testing tool, somebody sent us a link to this homemade meter, which tests for TDS, EC (electrical conductivity), PPM (parts per million).

EC/TDS/PPM Meter On Limited Budget – Link


  • Testing your own drinking water – Link

Gareth Branwyn

Gareth Branwyn is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of a dozen books on technology, DIY, and geek culture, including the first book about the web (Mosaic Quick Tour) and the Absolute Beginner’s Guide to Building Robots. He is currently working on a best-of collection of his writing, called Borg Like Me.



  1. Adam says:

    MAybe it’s just me, but it appears that something– perhaps the ‘buzz up’ code– is really breaking the formatting.

  2. Dale says:

    Just to clarify;

    PPM (parts per million)

    Is a unit of measurement not a water quality characteristic (hardness, turbidity, …) that is measured.

    The DIY conductivity meter will also do pH too (that’s how lab pH meters work), it looks like a cool project.

  3. jdkchem says:

    ppm of what? That would be rather important.

  4. Anonymous says:

    maybe Total organic carbon (TOC)

  5. Anonymous says:

    ppm is a measurement of quality as 0 ppm is pure H20. It doesn’t really matter what is causing the ppm values as the water company puts things in the water like fluorine and chlorine. in general any ppm values in tap water are considered impurities. You would need a mass spectrometer for example to find out exactly what and how much impurities are in the water. These are only at universities or big companies.

  6. Wayne Woodall says:

    ppm is the parts per million (or mg/L milligrams per litre) of total salt. The TDS can be calculated from the measured Electrical Conductivity. Commonly Electrical Conductivity in uS/cm (microsiemens per centimetre) multiplied by a factor of 0.65 (this factor can vary depending on the chemical compostiton of the water and its source) gives the TDS.

    Electrical conductivity is inversely related to the resistance of the water sample.