###### Abstract  
Water supply and sewage drainage pipes have a critical role to play in the provision of clean water and sanitation, and pipe material selection influences infrastructure life, water quality, and microbial communities. Zinc-containing compounds are highly valued due to their mechanical properties, anticorrosion behavior, and antimicrobial properties. However, the effect of zinc salts, such as zinc sulfate hepthydrate and zinc chloride, on biofilm-forming bacteria, including _Escherichia coli_ and _Enterococcus faecalis_, is not well established. This study investigates the antibacterial properties of these zinc salts under simulated pipeline conditions using minimum inhibitory concentration assays, biofilm production assays, and antibiotic sensitivity tests. Findings indicate that zinc chloride is more antimicrobial due to its higher solubility and bioavailability of Zn\({}^{2+}\) ions. At higher concentrations, zinc salts inhibit the development of a biofilm, whereas sub-inhibitory concentrations enhance the growth of biofilm, suggesting a stress response in bacteria. zinc chloride also enhances antibiotic efficacy against _E. coli_ but induces resistance in _E. faecalis_. These findings highlight the dual role of zinc salts in preventing biofilm formation and modulating antimicrobial resistance, necessitating further research to optimize material selection for water distribution networks and mitigate biofilm-associated risks in pipeline systems. water distribution systems; zinc salts; _Escherichia coli_; _Enterococcus faecalis_  
1  
Water supply and sewage drainage systems are crucial for providing safe and clean water and efficient sanitation. Pipe material selection is a fundamental component in determining not only the mechanical durability and lifespan of such systems but also their impact on water quality and microbial populations that develop in them. Of the various materials used in pipelines, metals such as iron, copper, and zinc are used as they are corrosion-resistant, mechanically strong, and possess natural antimicrobial properties. Zinc and its salts have been widely used in various applications, including galvanized steel paint,antifouling paint, and water treatment reagents, due to their ability to inhibit microbial contamination and biofilm formation [1]. Still, to the extent that the antimicrobial effect of zinc has been discovered, its impact on microbial communities and biofilm-forming bacteria, such as _Escherichia coli_ and _Enterococcus faecalis_, in water systems remains to be thoroughly researched [2]. Biofilm formation in water supply systems is a highly significant public health and infrastructure management issue. Biofilms consist of complex microbial populations embedded in an extracellular polymeric substance (EPS) matrix, which allows bacteria to adhere to surfaces, thereby aiding their survival and contributing to antimicrobial resistance [3]. Biofilm growth in pipes can reduce water flow efficiency, increase energy consumption, and accelerate material degradation, ultimately leading to corrosion, pipe failure, and an increased risk of contamination. Additionally, biofilm-related bacteria exhibit heightened resistance to disinfectants and antibiotics, making them even more challenging to destroy [4]. In metal pipes, biofilm growth can initiate localized corrosion and compromise material strength. Recent studies have shown that certain metals, including zinc, influence biofilm dynamics by either inhibiting or stimulating bacterial attachment, depending on their chemical composition, concentration, and interaction with bacterial metabolism [5; 6]. Zinc is an essential trace element for bacterial metabolism but exhibits antimicrobial properties at elevated concentrations by targeting several key biological processes. Specifically, zinc can inhibit metalloenzymes such as alcohol dehydrogenase and carbonic anhydrase, disrupting critical metabolic functions.