ISO 7887:2011

Overview

ISO 7887:2011 - Water quality - Examination and determination of colour - defines four standardized methods (A–D) to assess the colour of water. It distinguishes between apparent colour (visual, unfiltered sample) and true colour (measured after filtration through a 0.45 µm membrane). Methods C and D align with the traditional hexachloroplatinate colour scale; Method B uses instrumental spectrophotometric/filter-photometer measurement; Method A is a quick field visual check. Results must include which method (A–D) was used.

Key topics and technical requirements

• Methods A–D:
  • Method A: Visual examination of apparent colour in a clear bottle (field/rapid screening). Report intensity and hue (e.g., “pale, yellowish brown”).
  • Method B: True colour by optical instruments (spectrophotometer or filter photometer). Measure absorption at a minimum of three wavelengths (recommended 436 nm, 525 nm, 620 nm); report spectral absorption coefficient (α, in m⁻¹) and wavelength. Use optically pure water for reference.
  • Method C: True colour at 410 nm for comparison with potassium hexachloroplatinate/cobalt calibration; colour expressed in mg·L⁻¹ Pt.
  • Method D: Visual comparison with hexachloroplatinate standard solutions (traditional Pt scale).
• Sample handling: Filter for true-colour methods through a 0.45 µm membrane; store samples if needed (Method A: up to 5 days at 4 °C ±2 °C in the dark). Prevent aeration that could oxidize iron/manganese and change colour.
• Interferences: Suspended and colloidal matter, iron/manganese oxidation, pH changes and filtration artifacts can alter results - report turbidity or colloidal presence when filtration cannot yield a clear filtrate.
• Instrument specifics: Spectrophotometers (330–780 nm) or filter photometers with narrow bandwidths; use shorter pathlengths (down to 1 mm) or dilution for strongly coloured samples. Report bandwidth (Δλ) if non-monochromatic radiation is used.
• Quality & reporting: Annex A (quality control) and Annex B (precision data) provide internal QC and performance metrics. Always state the method used and relevant parameters (wavelength, absorption coefficient or mg·L⁻¹ Pt, pH).

Applications and users

ISO 7887 is applied by:

• Water utilities and treatment plant labs (raw and potable water colour monitoring)
• Environmental and limnological surveys
• Industrial and wastewater laboratories monitoring effluent colour
• Regulatory bodies and accredited testing labs for compliance and reporting

Practical benefits include consistent colour measurement for treatment optimization, source-water characterisation (DOC/SUVA correlations), and regulatory reporting.

Related standards

• ISO 3696 - Water for analytical laboratory use
• ISO 5667-3 - Water sampling: preservation and handling
• ISO 10523 - Determination of pH

Keywords: ISO 7887, water quality, colour determination, true colour, apparent colour, hexachloroplatinate, spectrophotometer, filter photometer, 410 nm, 436 nm, 0.45 µm filtration, DOC.