Water clarity criteria for bathing waters based on user perception

Abstract

Perception of bathing water quality has been studied by water-side surveying of bathers and/or by-standers. Bathing water quality assessment was strongly related to visual cues and, in particular, water clarity. A minimum water clarity (as measured by horizontal black disc sighting range y BD ) of 1·2 m (which corresponds to a Secchi disc depth of 1·5m) is required before a water is perceived, on the average, as suitable for bathing. If, for management purposes, it is required that 90% of people perceive a water clarity as suitable for bathing, then y BD needs to exceed about 2·2 m, corresponding to a Secchi disc depth of approximately 2·75 m. However, perception of water clearness appears to markedly affect a site's overall suitability for bathing only at low water clarities. In this study, perception of colour seems to be a minor factor, in part because the colour of the waters studied was very difficult to assess. Data for other factors, for example facilities present and litter, were also collected but could not be analysed in detail.