Why is it tested?
Because both are cheap and fast; when they change they are the first to reveal a problem that has not yet been named.
What does colour report?
According to WHO’s drinking-water guidelines, drinking-water should ideally have no visible colour. Colour is usually due to coloured organic matter (primarily humic and fulvic acids) associated with the humus fraction of soil.
But colour is also strongly influenced by iron and other metals, either as natural impurities or as corrosion products. It may also result from contamination of the source with industrial effluents and may be the first indication of a hazardous situation.
WHO’s advice is therefore not a limit but a behaviour: the source of colour in a drinking-water supply should be investigated, particularly if a substantial change has taken place.
The numerical reference rests on perception: most people can detect colour above 15 true colour units (TCU) in a glass of water, and levels below 15 TCU are often acceptable to consumers. WHO proposes no health-based guideline value for colour in drinking-water.
Coloured water has a further implication: according to WHO, high colour from natural organic carbon could also indicate a high propensity to produce by-products from disinfection processes.
What does conductivity measure?
Conductivity does not measure a contaminant directly; it measures the dissolved ion load of the water. That makes it a fast, practical proxy for total dissolved solids (TDS).
WHO has set no health-based guideline value for TDS; its assessment runs through palatability: the palatability of water with a TDS level of less than about 600 mg/l is generally considered to be good, and drinking-water becomes significantly and increasingly unpalatable at TDS levels greater than about 1000 mg/l.
High TDS has a second consequence, and for a facility it means cost: according to WHO, high levels of TDS may also be objectionable to consumers owing to excessive scaling in water pipes, heaters, boilers and household appliances.
In a pool, colour is a hard limit
While drinking-water has no health-based guideline value for colour, swimming pool regulation sets a number: Annex 2 of the Turkish Regulation on the Health Principles and Conditions Applicable to Swimming Pools defines colour as 10 units as Pt/Co and turbidity as 5 units as SiO₂ or Jackson units, with monthly measurement.
Colour carries a separate meaning in a pool: if the water is not clear the bottom cannot be seen, and that is a safety issue. Turbidity also makes it harder for the disinfectant to reach the microorganisms.
Sources
- [1] Guidelines for Drinking-water Quality — Chapter 10: Acceptability aspects — Dünya Sağlık Örgütü (WHO) (retrieved 1 September 2026)
- [2] Regulation on the Health Principles and Conditions Applicable to Swimming Pools (Official Gazette, 6 March 2011, No. 27866) — Resmî Gazete (retrieved 31 August 2026)
- [3] Regulation on Waters Intended for Human Consumption, Annex 1 (Official Gazette, 17 February 2005, No. 25730) — Resmî Gazete (retrieved 6 September 2026)
The medical and legal information in this article is taken from the sources listed above and is not diagnostic or treatment advice. Figures are reproduced as published in those sources.
