TDS is one of the most commonly quoted water quality numbers, and one of the most commonly misunderstood. This guide explains what total dissolved solids are, how they are measured and what a reading does — and does not — say about your water.
TDS stands for total dissolved solids: the combined quantity of all inorganic salts and small amounts of organic matter dissolved in water. It is normally expressed in milligrams per litre (mg/L) or, equivalently, parts per million (ppm). TDS is a bulk measurement — a single number covering everything dissolved, without identifying what those substances are.
Suspended particles are not included: sediment you can see is not dissolved, so it does not register as TDS. Dissolved gases are also excluded.
The laboratory method evaporates a filtered water sample and weighs the residue that remains. This is accurate but slow. In practice, most people use a handheld meter, which measures electrical conductivity and converts it to an estimated TDS value using a conversion factor.
A TDS meter measures how easily an electrical current passes through the water. Dissolved ions conduct electricity, so more dissolved salts generally means higher conductivity. The meter then applies a fixed multiplier to display a TDS figure. This is an estimate: substances that do not ionise are effectively invisible to the meter, and the conversion factor assumes a typical mix of salts that may not match your water.
A high reading means there is a relatively large quantity of dissolved material in the water. That can be entirely natural — groundwater that has passed through mineral-rich rock will have higher TDS than desalinated water — or it can indicate a change worth investigating. A reading on its own does not identify the source or the composition, so it is best used as a screening tool and a way to track change over time.
No. TDS does not determine whether water is safe to drink. It is an aggregate figure that cannot distinguish between harmless minerals and substances of concern, and it does not detect bacteria, most pesticides, or many organic compounds. Do not treat any specific TDS number as a pass or fail for safety.
A low TDS reading can coexist with a microbiological problem, and a high reading may simply reflect naturally mineral-rich water. Safety assessments require testing for specific parameters through a laboratory, alongside the official quality data for your supply area.
TDS does correlate with taste. Mineral-rich water is often described as full or slightly bitter, while very low TDS water is often described as flat. Taste preference is personal, and there is no universally correct level — some people prefer the crispness of low-TDS filtered water and others prefer mineral content.
Reverse osmosis is the household technology most associated with TDS reduction, because an RO membrane rejects a large proportion of dissolved salts. This is why suppliers often demonstrate systems with a TDS meter: the before-and-after difference is easy to see. It is a legitimate demonstration of membrane function, but remember that it shows dissolved salt reduction rather than proof of overall water safety. Read how reverse osmosis works.
The two are related but not the same. Hardness counts only calcium and magnesium; TDS counts everything dissolved. Water can have high TDS and low hardness if the dissolved content is mostly sodium salts. Softeners exchange hardness minerals for sodium, so they change hardness while leaving TDS broadly similar.
| Term | What it tells you |
|---|---|
| TDS | Total dissolved solids, as a single aggregate figure |
| pH | Acidity or alkalinity of the water |
| Hardness | Mainly dissolved calcium and magnesium |
| Chlorine | Residual disinfectant present in the supply |
| Conductivity | How easily current passes through water; used to estimate TDS |
Key takeaways
TDS is a quick, cheap and useful indicator, particularly for tracking change or checking that a membrane is still performing. It is not a substitute for proper testing. Once you know what you want to reduce, you can compare water filtration companies in Cyprus and discuss the appropriate system with suppliers.
Drinking water covers a wide range of TDS values depending on its source, and there is no single normal figure. Very low values are typical of desalinated or reverse osmosis water, while groundwater is usually higher. Because TDS does not identify individual substances, no specific number should be treated as a safety threshold.
Not necessarily. Low TDS mainly means fewer dissolved salts, which many people find tastes cleaner but others find flat. It is a taste and treatment indicator rather than a measure of quality on its own.
No. Boiling removes some dissolved gases and can address microbiological concerns, but dissolved solids remain — and as water evaporates the concentration can actually increase.
No. A TDS meter responds to dissolved ionic content. It cannot detect bacteria, and it is not a reliable way to measure residual chlorine or most organic compounds.
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Keep reading
How water filters work, the main system types used in Cyprus homes and businesses, what filtration can and cannot remove, and how to choose a system and a supplier.
What determines drinking water quality in Cyprus, why water can taste different between buildings, and when households consider additional filtration.
How reverse osmosis membranes separate dissolved substances from water, what an RO system is made of, what maintenance it needs and where it fits in a home.
A practical side-by-side comparison of reverse osmosis and standard water filters: filtration method, contaminants, taste, minerals, water use, installation, maintenance and cost.
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