Trend Analysis of Water Quality Parameters in a Selected Distribution System

Abstract

AbstractRapid urbanization poses tremendous challenges to meet the increased water demands in Chattogram city, the second-largest city in Bangladesh. Apart from the quantity, the distributed water quality in many cases fails to meet the permissible level. This study aimed to conduct a water quality trend analysis in a selected distribution system using a field survey to validate secondary datasets. Water sampling points were determined by applying the Analytical Hierarchical Process (AHP) technique under ArcGIS considering pipe leakage, source water quality, pipe age, and pipe materials. The study area comprises 397 km of pipes; among them, pipe material distribution comprises PVC (71.28%), asbestos (20.94%), mild steel (5.16%), ductile iron (2.17%), and cast iron (0.45%). The identified study network was established in 1963, 20.87% of pipes aged greater than 30 years, 15.07% in 20–30 years, 26.38% are in 10–20 years, and 37.68% of pipelines are relatively new, i.e., within 0–10 years. Historical data for the eight water quality parameters, i.e., pH, temperature, turbidity, BOD5, total coliform, fecal coliform, chloride, and residual chlorine, were collected from the secondary source and cross-checked by field survey. Compare to the source water quality, and distribution showed variations despite the seasonal variations, i.e., pre-monsoon (March to May), monsoon (June to October), and post-monsoon (November to February). Water Quality Index (WQI) values were computed using an interpolation technique, i.e., Inverse Distance Weighted (IDW) method, to generate a WQI map. Since 2016, mostly drinking water supplies showed an acceptable level, quality starts below standard in few places since 2017. Thus, the poor quality extends 17%, 21%, and 26% of the distribution lines in 2018, 2019, and June 2020, respectively. Therefore, this study suggests that water quality parameters are influenced by inadequate and centralized chlorination, physical damage of pipes, the absence of a sewer system within the city, the pipeline positioned close to the soak pits or open drains, and pressure fluctuation and lack of proper maintenance.KeywordsTrend analysisAnalytical hierarchical process (AHP)Water quality index (WQI)Inverse distance weighted (IDW)