Prediction of lead concentration at consumer tap of lead contaminated water supply system in high-rise buildings

Lead (Pb) is a toxic metal that can be present in drinking water; exposure to lead (WHO standard C < 10 μg/l) can result in learning deficits in children and increased blood pressure in adults. In 2015 a public outcry was caused by high excess lead concentrations found in the drinking water of public rental housing estates in Hong Kong. Similar incidents have been reported elsewhere. Drinking water supply systems in densely populated high-rise buildings consist of complex labyrinths of copper piping fitted with solder joints and brass fixtures that contain lead. The prediction of lead concentration at the consumer tap is most challenging: the lead release mechanism due to galvanic corrosion and the interaction with the diffusion and transport in the pipe flow is largely unknown; the accurate measurement of the low concentrations of concern is also demanding and costly. This paper presents a comprehensive experimental and theoretical investigation of lead contamination and transport in high rise buildings. Systematic tests on full-scale water supply chains dismantled from public rental housing estate buildings are performed. The main lead sources are determined; leaching experiments are performed on the key components to study the Pb leaching rate (R_t) over time. A 3D diffusion model is developed to model the leaching process assuming a constant Pb concentration next to the pipe wall (E₀), and the subsequent tap water concentration under flowing condition for a real-life water supply chain is successfully predicted by a numerical solution of the contaminant transport for the first time.