🎨 Water Colour
In short
Examination and determination of water colour by the four methods of the standard: A — visual assessment of apparent colour, B — true colour as the absorption coefficient at 436, 525 and 620 nm, C — true colour in mg/l Pt from the absorbance at 410 nm, D — visual comparison with hexachloroplatinate standard solutions. The test is performed according to PN-EN ISO 7887:2012; Methods: A — apparent colour, visually; B — true colour, absorption coefficient; C — true colour in mg/l Pt at 410 nm; D — visual comparison with hexachloroplatinate solutions (clause 1). The procedure comprises 7 steps; it is used for: Drinking water — descriptive requirement “acceptable to consumers and with no abnormal change” (Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 1), without a numerical value, Monitoring of surface water and groundwater — indicator 3.1.3 “Colour”, spectrophotometric and visual methodology according to PN-EN ISO 7887 (Journal of Laws 2021, item 1576, Annex 8), Raw water and drinking water — methods B, C and D (clause 1).
At a glance
- Standard: PN-EN ISO 7887:2012
- Category: Physicochemistry
- Procedure steps: 7
- Methods: A — apparent colour, visually; B — true colour, absorption coefficient; C — true colour in mg/l Pt at 410 nm; D — visual comparison with hexachloroplatinate solutions (clause 1)
- Wavelengths — method B: 436 nm (always), 525 nm and 620 nm; result in m⁻¹, rounded to 0.1 m⁻¹ (5.2, 5.9)
- Wavelength — method C: 410 nm; spectrophotometer with a bandwidth of 5 nm or filter photometer with a bandwidth of about 20 nm (6.4)
Overview
STATUS (as of 29.10.2026). PN-EN ISO 7887:2012 — Polish version, published 06.02.2015, implements EN ISO 7887:2011 and ISO 7887:2011 [IDT]; it replaced PN-EN ISO 7887:2002. The standard is current. The national amendment PN-EN ISO 7887:2012/Ap1:2015-06 changes one word in Annex A (A.3.1: “92 mg”, not “92 g” of humic acid); it does not change the procedure of methods A–D. ISO 7887:2011 is the third edition (16.12.2011), which replaced ISO 7887:1994; there is no newer edition.
SCOPE (clause 1). Method A — examination of apparent colour by observing the sample in a bottle; it gives only preliminary information (e.g. in field work) and allows only the apparent colour to be reported. Method B — determination of true colour with an optical instrument; for raw and drinking water and for industrial water of low colour. Method C — determination of true colour with an optical instrument by reference to the hexachloroplatinate concentration at λ = 410 nm. Method D — determination of colour by visual comparison with hexachloroplatinate standard solutions; for raw and drinking water. Methods C and D are harmonized with the traditional hexachloroplatinate scale; methods A and B are appropriate when the hue of the sample differs from the hue of the matching solutions. The method used (A–D) is stated with the result.
DEFINITIONS (clause 3). Apparent colour — colour due to dissolved substances and undissolved suspended matter, determined in the original sample without filtration or centrifugation. True colour — colour due only to dissolved substances, determined after filtration of the sample through a membrane filter of pore size 0.45 µm.
INTERFERENCES (5.3, 6.2). Suspended matter is removed by filtration through a 0.45 µm filter, but filtration itself can change the colour: contact with air causes oxidation and precipitation (e.g. iron and manganese compounds are retained on the filter or converted into a differently coloured oxidized form). If the filtrate remains turbid (clay colloids), this is stated in the test report. Clogging of the filter pores increases the retention of humic colloids and lowers the colour. Colour often depends on pH, so the pH of the filtrate is measured in parallel.
LEGAL REQUIREMENTS. Drinking water: the regulation of the Minister of Health of 22 May 2026 (Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 1) gives for colour the descriptive requirement “acceptable to consumers and with no abnormal change” — without a numerical value. The repealed regulation of 2017 (Journal of Laws 2017, item 2294) had the same requirement with the explanatory note “desirable value of this parameter in water at the consumer’s tap — up to 15 mg Pt/l”; the regulation of 2015 (Journal of Laws 2015, item 1989) gave only the descriptive requirement. Annex 4 Part B item 7 gives for colour a measurement uncertainty of 30 %, and Annex 3 lists colour among the group A parameters. Monitoring of surface water and groundwater: PN-EN ISO 7887 is the spectrophotometric and visual methodology for indicator 3.1.3 “Colour” (Journal of Laws 2021, item 1576, Annex 8).
WHAT WE DO NOT GIVE HERE. The publicly available text of the standard covers clauses 1–5 and method C up to 6.7.1 (determination of the specific absorption coefficient of the calibration solution). We do not give the procedure of method D, the quality control procedure (Annex A) or the precision data (Annex B); the equation for calculating colour in method C is given in the form used in the textbook “Chemia wody” (Wrocław University of Science and Technology, 2024, section 4.3), which describes method C according to EN ISO 7887:2011.
Method principle
Method A (clause 4): the shaken, unfiltered sample in a colourless bottle is examined in diffused light against a white background, after any suspended matter has settled, and the intensity of the colour (nil, pale, light, dark) and the hue are stated, e.g. “apparent colour in accordance with ISO 7887, method A: pale, yellowish brown”.
Method B (clause 5): true colour is characterized by the attenuation (absorption) of light by the filtered sample, measured with a spectrophotometer or a filter photometer at no fewer than three wavelengths of the visible range: λ1 = 436 nm (always), λ2 = 525 nm and λ3 = 620 nm. The result is the spectral absorption coefficient α(λ) = A · f / d in m⁻¹ (A — absorbance, d — optical path length in mm, f = 1000), rounded to 0.1 m⁻¹ and reported with the wavelength and the pH of the filtrate.
Method C (clause 6): the intensity of the yellowish brown colour of the filtered, optically clear sample is determined from the absorbance at λ = 410 nm and compared with the specific absorption coefficient of a calibration solution of potassium hexachloroplatinate and cobalt chloride at the same wavelength — the result in mg/l Pt. The wavelength of 410 nm is the shortest wavelength at which the absorption spectra of a natural water rated by method D at 100 mg/l Pt and of the matching calibration solution of 100 mg/l Pt intersect.
Method D (clause 7): visual comparison of the colour of the sample with hexachloroplatinate standard solutions (procedure outside the available text of the standard).
Applications
- Drinking water — descriptive requirement “acceptable to consumers and with no abnormal change” (Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 1), without a numerical value
- Monitoring of surface water and groundwater — indicator 3.1.3 “Colour”, spectrophotometric and visual methodology according to PN-EN ISO 7887 (Journal of Laws 2021, item 1576, Annex 8)
- Raw water and drinking water — methods B, C and D (clause 1)
- Industrial water of low colour — method B (clause 1)
- Field work — preliminary assessment of apparent colour by method A (clause 1)
Key parameters
| Parameter | Value |
|---|---|
| Methods | A — apparent colour, visually; B — true colour, absorption coefficient; C — true colour in mg/l Pt at 410 nm; D — visual comparison with hexachloroplatinate solutions (clause 1) |
| Wavelengths — method B | 436 nm (always), 525 nm and 620 nm; result in m⁻¹, rounded to 0.1 m⁻¹ (5.2, 5.9) |
| Wavelength — method C | 410 nm; spectrophotometer with a bandwidth of 5 nm or filter photometer with a bandwidth of about 20 nm (6.4) |
| Cells — method C | glass or quartz, optical path length 40 mm or 50 mm; 10 mm for strongly coloured samples (6.4.1) |
| Filtration | 0.45 µm membrane filter before methods B and C; pH of the filtrate measured in parallel (5.7, 6.6) |
| Sample storage | examination as soon as possible; if storage is unavoidable — up to 5 days in the dark at (4 ± 2) °C, without aeration (4.2) |
Standard
- Standard number
- PN-EN ISO 7887:2012
- Title (PL)
- Jakość wody — Badanie i oznaczanie barwy
- Title (EN)
- Water quality — Examination and determination of colour
Step-by-step procedure
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Sampling and sample storage
Collect the sample in a colourless bottle and examine it as soon as possible; if storage is unavoidable — up to 5 days in the dark at (4 ± 2) °C, avoiding aeration, especially when colour-changing redox reactions are possible (4.2).
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Method A — apparent colour
Shake the sample, pour it unfiltered into a bottle and, after the suspended matter has settled, examine it in diffused light against a white background; state the intensity of colour and the hue (4.3–4.4).
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Filtration (methods B and C)
Filter the sample through a 0.45 µm membrane filter; in method C let the filtrate reach room temperature. Measure the pH of the filtrate in parallel with each colour determination (5.7, 6.6).
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Strongly coloured samples
Dilute the filtrate with a measured volume of optically pure water into the calibration range (measure the pH before and after dilution) or, without dilution, use a cell with a suitably shorter optical path length (5.7, 6.6).
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Method B — measurement
Measure the absorbance at 436 nm against optically pure water in the reference cell, then at 525 nm and 620 nm; calculate α(λ) = A · 1000 / d in m⁻¹, take the dilution into account and report the result with the wavelength, the bandwidth and the pH (5.7–5.9).
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Method C — specific absorption coefficient
Measure the absorbance A410 of the 100 mg/l Pt calibration solution against optically pure water and calculate the specific absorption coefficient a = A410 / (100 · d) in mm⁻¹ · (mg/l Pt)⁻¹, d — optical path length in mm (6.7.1; form of the equation according to the Wrocław University of Science and Technology textbook, section 4.3).
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Method C — measurement and result
Measure A410 of the filtrate against optically pure water and calculate the true colour C = A410 / (a · d) in mg/l Pt (Wrocław University of Science and Technology textbook, section 4.3); state the method used with the result and record any turbidity of the filtrate in the test report (clause 1, 6.2).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Colourless bottles | for sampling and method A, according to ISO 5667-3; glassware in contact with the sample washed with hydrochloric acid of about 2 mol/l or with a laboratory detergent solution and rinsed with water for washing (4.1) | — |
| Spectrophotometer or filter photometer | method B: visible range (about 330–780 nm), preferably double-beam with a bandwidth of 10 nm, or a filter photometer with 436, 525 and 620 nm filters with a bandwidth of about 20 nm; method C: measurement at 410 nm, bandwidth 5 nm (5.5, 6.4) | — |
| Cells | method C: 40 mm or 50 mm, 10 mm for strong colour; method B: if α is below 0.1 cm⁻¹, optical path length of at least 10 mm, for strong colour down to 1 mm (5.7, 6.4.1) | — |
| Membrane filtration assembly | filters of pore size 0.2 µm (for preparing optically pure water) and 0.45 µm (for samples) (5.5.3, 6.4.3) | — |
| pH meter | pH of the filtrate according to ISO 10523, in parallel with each colour determination (5.5.4, 5.7) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Optically pure water | — | soak a 0.2 µm membrane filter for about 1 h in distilled or deionized water, pass about 1 l of grade 1 water according to ISO 3696 through it, discarding the first 50 ml of filtrate; freshly distilled or deionized water without measurable absorbance is also suitable (5.4.1) |
| Water for washing | — | grade 3 according to ISO 3696 (5.4.2) |
| Potassium hexachloroplatinate(IV), K₂PtCl₆ | 16921-30-5 | for the stock calibration solution; a sensitizer and toxic compound (6.3.1) |
| Cobalt(II) chloride hexahydrate, CoCl₂·6H₂O | 7791-13-1 | for the stock calibration solution (6.3.1) |
| Hydrochloric acid, ρ = 1.18 g/ml | 7647-01-0 | (100 ± 1) ml per 1000 ml of stock calibration solution (6.3.1) |
| Stock colour calibration solution, 500 mg/l Pt | — | dissolve (1.245 ± 0.005) g of K₂PtCl₆ and (1.000 ± 0.005) g of CoCl₂·6H₂O in about 500 ml of optically pure water, add (100 ± 1) ml of hydrochloric acid and make up to 1000 ml in a volumetric flask; store in the dark at (4 ± 2) °C in a well-stoppered dark brown glass bottle — stable for at least 3 years (6.3.1) |
| Colour calibration solution, 100 mg/l Pt | — | transfer 20 ml of the stock solution by pipette into a 100 ml volumetric flask and make up with optically pure water; in a well-stoppered bottle in the dark at (4 ± 2) °C stable for at least 1 month (6.3.2) |
Health and safety (OHS)
- Potassium hexachloroplatinate is a sensitizer and a toxic compound — use protection when handling it (6.3.1)
- Hydrochloric acid and cobalt(II) chloride are handled according to the safety data sheets
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 7887:2012 — “Water quality — Examination and determination of colour”.
How does this method work?
Method A (clause 4): the shaken, unfiltered sample in a colourless bottle is examined in diffused light against a white background, after any suspended matter has settled, and the intensity of the colour (nil, pale, light, dark) and the hue are stated, e.g.
What is the measuring range and accuracy?
Methods: A — apparent colour, visually; B — true colour, absorption coefficient; C — true colour in mg/l Pt at 410 nm; D — visual comparison with hexachloroplatinate solutions (clause 1); Wavelengths — method B: 436 nm (always), 525 nm and 620 nm; result in m⁻¹, rounded to 0.1 m⁻¹ (5.2, 5.9); Wavelength — method C: 410 nm; spectrophotometer with a bandwidth of 5 nm or filter photometer with a bandwidth of about 20 nm (6.4); Cells — method C: glass or quartz, optical path length 40 mm or 50 mm; 10 mm for strongly coloured samples (6.4.1).
How long does the test take?
The procedure comprises 7 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Colourless bottles, Spectrophotometer or filter photometer, Cells, Membrane filtration assembly, pH meter.
Where is this test used?
Drinking water — descriptive requirement “acceptable to consumers and with no abnormal change” (Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 1), without a numerical value; Monitoring of surface water and groundwater — indicator 3.1.3 “Colour”, spectrophotometric and visual methodology according to PN-EN ISO 7887 (Journal of Laws 2021, item 1576, Annex 8); Raw water and drinking water — methods B, C and D (clause 1); Industrial water of low colour — method B (clause 1); Field work — preliminary assessment of apparent colour by method A (clause 1).
What safety precautions apply?
Potassium hexachloroplatinate is a sensitizer and a toxic compound — use protection when handling it (6.3.1); Hydrochloric acid and cobalt(II) chloride are handled according to the safety data sheets.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 7887.