Water quality trend analysis in a citywide water distribution system Keya Chowdhury and Aysha Akter * Dept of Civil Engineering, Chittagong University of Engineering & Technology (CUET), Chittagong 4349, Bangladesh *Corresponding author. E-mail: aysha_akter@cuet.ac.bd AA, 0000-0002-5730-1379 ABSTRACT Rapid urbanization poses challenges to meet the increased water supply demands. Apart from the quantity, the distributed water quality often fails to meet the permissible level. This study aimed to conduct a citywide spatio-temporal variation of water quality parameters. Water sampling points were selected by applying the Analytical Hierarchical Process (AHP) technique using ArcGIS considering pipe leakage, source water quality, pipe age, and pipe materials. The Chattogram city comprises 397 km of pipes; pipe material distribution shows 71.28% PVC, 20.94% asbestos, 5.16% mild steel, 2.17% ductile, and 0.45% cast iron. The citywide pipe network was established in 1963; 20.87% of pipes aged over 30 years, 15.07% 20–30 years, 26.38% 10–20 years, and 37.68% pipelines are relatively new, i.e., within 0–10 years. Eight water quality parameters, i.e., pH, temperature, turbidity, biochemical oxygen demand after five days (BOD 5 ), total coliform, fecal coliform, chloride, and residual chlorine, were collected from the secondary source cross-checked by field survey. Computation of the Water Quality Index (WQI) was interpolated using Inverse Distance Weighted (IDW) method to generate a WQI map. Thus, this study could be a basis to improve the treatment system and proper distribution network maintenance. Key words: Analytical Hierarchical Process (AHP), pipe physical properties, water distribution network, Water Quality Index (WQI) HIGHLIGHTS • Spatio-temporal variation of water quality parameters in the citywide distribution system. • Water sampling locations were identified using the Analytical Hierarchical Process (AHP). • Inverse Distance Weighted (IDW) method to generate a Water Quality Index (WQI) map. INTRODUCTION The drinking water quality complications are severe in the city due to rapid urbanization. About 500 million urban occupants around the world face inappropriate access to water services or experience water scarcity. The remaining 5.2 billion people have access to an ‘improved’ water source; nevertheless, they drink unsafe water following contamination at the intake, then in the piped distribution system, and unhygienic handling during transport (USAID 2006). Parveen et al. (2008) reported that world- wide at least one and a half thousand million people use polluted water. Cities in developing countries often face acute waterborne diseases. Due to exposure to extreme pH values, human health suffers from eye irritation, skin rashes, and mucous membrane infection. Water temperature plays a vital role in determining water acceptability for human consumption and use (WHO 1996b). In association with the aesthetics and tastes, drinking water turbidity is linked to gastrointestinal illness due to human consumption. Annually a current global population of 6.5 billion gastroenteritis cases has been reported (Nath et al. 2006; Parveen et al. 2008). Biochemical oxygen demand after five days (BOD 5 ) is usually tested for wastewater treatment to provide information on the biologically convertible proportion of the organic content of a water sample. Traces of BOD 5 in drinking water would pose a severe threat to the human body (Al-Ananzeh et al. 2010; Al-Ananzeh 2021; McKee & Cruz 2021). On the other hand, total coliform in drinking water increases the risk of waterborne illness. The thermotolerant coliform group (fecal coliform) in subtropical or tropical waters is enriched with organic waste by humans and wild animals, including birds (New York State Department of Health 2002; McKee & Cruz 2021). Therefore, positive fecal coliform results, i.e., posi- tive E. coli results, should indicate fecal pollution. Apart from taste, chloride toxicity so far is not recorded for humans except in the case of impaired sodium chloride metabolism (viz. in congestive heart failure) (WHO 1996a; McKee & Cruz 2021). This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). © 2021 The Authors Water Science & Technology Vol 00 No 0, 1 doi: 10.2166/wst.2021.342 corrected Proof Downloaded from http://iwaponline.com/wst/article-pdf/doi/10.2166/wst.2021.342/940920/wst2021342.pdf by guest on 29 September 2021