What Is TDS in Drinking Water?

TDS (total dissolved solids) explained: what a TDS meter measures, what it does not tell you, and how to use the number without overreacting.

Direct answer

TDS means total dissolved solids — the amount of dissolved minerals, salts, and similar substances in water, usually reported in mg/L or ppm. A cheap TDS meter estimates this from electrical conductivity. It is a useful screening number, but it does not identify bacteria, lead, pesticides, or which mineral is present.

What TDS includes

Typical contributors are calcium, magnesium, sodium, potassium, chloride, sulfate, bicarbonate, and small amounts of other dissolved substances. Hard water often has higher TDS because of calcium and magnesium. Seawater has very high TDS; rain and distilled water are very low.

What a home TDS meter cannot do

It cannot prove water is safe or unsafe
It cannot detect microbes
It cannot measure lead or arsenic specifically
Two waters with the same TDS can have very different chemistry

Use TDS as a trend tool — for example to see if an RO system is still reducing dissolved solids — not as a complete water test.

How to read the number

Guidance ranges exist for taste and general mineralisation, but “good TDS” depends on context. Very low TDS can taste flat. High TDS can taste salty or bitter and may correlate with scaling. For health-related contaminants you need a proper lab or utility report, not a pocket meter alone.

Practical uses

Compare tap water vs RO product water in the same home
Notice a sudden jump that may mean a filter or membrane needs attention
Avoid treating a pleasant mid-range TDS as automatically “bad”

Educational overview. Local standards, lab methods, and reports differ. Use official reports and qualified local advice for decisions about your supply. About Water Omnis · Privacy.