Make:

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

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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.

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ppm of what? That would be rather important.

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maybe Total organic carbon (TOC)

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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.

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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.

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