Electrical Conductivity as an Indicator to Assess the Suitability of River Water for Recreational Use

Urban rivers flowing through cities are places of recreation and relaxation for citizens. However, these rivers are sometimes contaminated by Escherichia coli (E. coli). Therefore, the purpose of this study was to develop a simple method to investigate E. coli contamination in river water. From May to October 2019, water samples were collected from five locations in the Toga River in Kobe City, Japan, and the fecal coliform density (FCD) was measured, along with the electrical conductivity and the chloride ion concentration of the river water. Comparison of these water quality parameters with actual fecal coliform densities revealed a high correlation between electrical conductivity and FCD. Whereas, little correlation was found between FCD and chloride concentration. Receiver operating characteristic (ROC) analysis was used to evaluate the method that uses the electrical conductivity as an estimating parameter. The area under the curve (AUC) was used as a measure of the performance of the ROC curve algorithm. The calculated AUC value stayed high, above 0.95, over a wide range of FCD values, suggesting that this rapid monitoring method is appropriate for assessing the quantity of contaminating fecal coliforms in the range higher than 300/100 mL