TDS in Tap Water UK: Total Dissolved Solids Explained

What are Total Dissolved Solids?

TDS (Total Dissolved Solids) is a measure of everything dissolved in your water — minerals, salts, metals, and organic compounds. It's expressed in mg/l (same as ppm) and gives you an overall picture of your water's mineral content.

TDS is closely related to water hardness, but it's broader. While hardness measures only calcium and magnesium, TDS includes all dissolved substances: sodium, potassium, bicarbonates, chlorides, sulphates, and trace elements.

What is a Normal TDS Level?

The WHO classifies drinking water TDS as:

  • Excellent: below 300 mg/l
  • Good: 300-600 mg/l
  • Fair: 600-900 mg/l
  • Poor: 900-1200 mg/l

Most UK tap water falls in the 100-400 mg/l range. Hard water areas (South East England) tend to have higher TDS, while soft water areas (Scotland, Wales) have lower TDS.

Does TDS Matter?

For taste: TDS is one of the biggest factors in how water tastes. Bottled mineral waters advertise their TDS and mineral profile. Very low TDS water tastes flat, while moderate TDS water tastes clean and refreshing.

For coffee and tea: TDS affects extraction. The SCA recommends brewing water with TDS of 75-250 mg/l for optimal coffee flavour.

For health: TDS alone doesn't indicate safety. It's the individual components that matter. UK water companies test for each regulated substance separately.

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Frequently Asked Questions

What is TDS in water?

TDS stands for Total Dissolved Solids — the total amount of minerals, salts, and organic matter dissolved in water, measured in milligrams per litre (mg/l) or parts per million (ppm). It includes calcium, magnesium, sodium, potassium, bicarbonates, chlorides, and sulphates.

What is a good TDS level for drinking water?

The WHO considers TDS below 300 mg/l as "excellent" for drinking water, 300-600 mg/l as "good", 600-900 mg/l as "fair", and above 1200 mg/l as "unacceptable". Most UK tap water has TDS between 100-400 mg/l depending on the region and water hardness.

Does TDS affect water taste?

Yes. Very low TDS water (below 50 mg/l) can taste flat or bland. Water with TDS of 100-400 mg/l generally tastes pleasant, as the dissolved minerals contribute to flavour. Very high TDS (above 500 mg/l) may taste salty or mineral-heavy.

Is high TDS water dangerous?

High TDS itself is not dangerous — it simply means more dissolved minerals. However, what matters is which specific substances make up the TDS. UK water companies monitor individual parameters (lead, nitrate, etc.) separately. The TDS measurement is primarily an indicator of overall mineral content, not safety.

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