Accurate quantification of colour in water samples is critical, as it strongly influences light penetration in receiving waters and consequently affects primary production and ecosystem balance. Despite its importance, water colour is often underrepresented due to limitations in existing measurement methods. In this study, the ability of conventional spectrophotometric methods to represent apparent colour was evaluated using 403 water samples with colour intensities ranging from 11 to 12,325 Platinum-Cobalt (Pt-Co) units. An Archimedean spiral was employed to visualise the representational limitations of four commonly applied methods: Pt-Co, Spectral Absorption Coefficient (SAC), American Dye Manufacturers’ Institute (ADMI), and Area method. All methods exhibited weaknesses, primarily because they rely on absorbance at specific wavelengths. In particular, the widely used Pt-Co method failed to adequately capture certain types of colour pollution, especially grey, black, and blue hues. To overcome these limitations, a novel digital image-based method was developed and tested using the same dataset. The proposed method showed significantly improved alignment with apparent colour, particularly for the RGB colour space indicating an enhanced ability to capture variations in colour intensity across samples, resulting in a more informative representation of colour variability compared with Pt-Co measurements. Moreover, methodological limitations and measures for standardising the digital-image-based method were also addressed in order to reduce uncertainty and increase comparability. The findings of this study demonstrate that digital image-based colour analysis has strong potential for quantifying colour pollution in water, and also has further promise for real-time monitoring. • Spectrophotometric methods may underestimate risks of colour pollution • Current methods show limited responsiveness to diverse colour ranges • Pre-treatment in spectrophotometric methods causes loss of dye and colour • Digital image-based method preserves colour fidelity without filtration • Digital image-based method is sensitive to all colours, aligning with perception
Hocaoglu et al. (Mon,) studied this question.