What is a TDS meter and how does it work?

A TDS meter is basically a electrical charge (EC) meter whereby two electrodes equally spaced apart are inserted into water, and used to measure charge. The result is interpreted by the TDS meter and converted into a ppm figure. If water contains no soluble materials and is pure, it will not conduct a charge and will therefore have a 0 ppm figure. Conversely, if the water is full of dissolved materials, it will conduct a charge, with the resulting ppm figure being proportional to the amount of dissolved solids. This is because all dissolved solids have an electrical charge, which allows conduction of electrical charge between the electrodes.

In reality, the most accurate way to measure TDS of water in a laboratory setting would be to boil the water until there is none remaining, and then to weigh the remaining material. This of course is totally impractical for the lay person, as accurate scales and special equipment would be required to achieve such measurements. The TDS meter is therefore the next best device to achieving an estimated TDS reading.