What a TDS Meter Tells You About Your Water

What the number measures

TDS stands for total dissolved solids. It includes dissolved minerals and salts in the water. A handheld meter estimates that total from electrical conductivity and usually displays a number in parts per million.

It is useful for seeing a change. It does not name the substances in the water or tell you which one caused the reading.

Why mineral-rich water has a reading

Groundwater picks up minerals as it moves through rock. That can raise TDS without telling you whether a particular contaminant is present. EPA lists TDS under its secondary drinking-water guidance, which addresses taste and other everyday water characteristics.

Think of TDS as one measurement in a larger picture. Your utility report and tests for specific questions provide the detail.

Softening and RO change water differently

A softener exchanges calcium and magnesium for sodium or potassium. It removes hardness without removing all dissolved solids, so a TDS reading alone cannot prove that softening failed.

RO separates water through a membrane and reduces dissolved solids. Comparing feed water and RO water can help track membrane performance. Use the system’s instructions and a consistent sampling method.

A simple RO comparison

If feed water reads 300 ppm and the RO tap reads 30 ppm, the estimated TDS reduction is 90 percent: subtract 30 from 300, divide by 300 and multiply by 100.

That is a TDS comparison. A specific contaminant result needs its own test. Compare your readings over time and ask about service if the change no longer matches the system’s expected performance.

Choose the test and treatment together

For scale, measure hardness. For disinfectant taste, check chlorine or chloramine. For a named contaminant, use utility data or a laboratory test.

Then choose the treatment for the job. Compare softening, carbon and RO or book a free assessment to talk through everyday water problems.