Satellite remote sensing to improve source water quality monitoring: A water utility's perspective

Polyphytos Reservoir provides the city of Thessaloniki with efficient and safe drinking water after appropriate treatment at the Thessaloniki Drinking Water Treatment Plant (TDWTP). This study evaluates the feasibility of utilizing open access satellite imagery and analysis tools to continuously, rapidly, at a low cost and precisely evaluate the water quality of large reservoirs like Polyphytos Reservoir. Thereby, more than 300 satellite images were analyzed, spanning a 9-year period from 2013 to 2022, using specific algorithms designed for determining surface water quality, such as Se2WaQ, NDWI and Oil Spill Index (OSI). These algorithms were used to estimate chlorophyll concentration (Chl-a), turbidity values (Tur) and hydrocarbon (OSI) presence. The generated results are compared with data records regarding the reservoir's water level and chlorophyll and turbidity measurements in the reservoir and at the inlet of the TDWTP. This study shows that the examined satellite survey tools can effectively identify unanticipated formations on the surface of the reservoir and provide a quantitative assessment of the surface water quality using insitu sampling for algorithms validation. The findings of the study were used to create a workflow that can serve as a guide for end-users interested in a low-cost, quick, continuous, and accurate surface water quality assessment of large reservoirs, using satellite remote sensing tools. It is anticipated that the information provided in this study would be useful to end-users community.