Lead (Pb) is a heavy metal that may be present in household drinking water supply systems containing leaded components. Pb exposure can affect the development of the nervous system and brain in children and cause serious health problems in adults. Worldwide, lead water crisis have been reported in Washington D.C., Flint (Michigan, USA), Scotland, and Hong Kong. The lead contamination problem in drinking water is a global public issue that has been studied for decades. While the majority of incidents were caused by lead service lines used in water supply systems, lead contamination from lead solder joints and brass fittings is becoming an emerging problem in modern cities. Water supply chains in high-rise buildings are long and torturous with distributed small-size lead sources. The lead...[ Read more ]

Lead (Pb) is a heavy metal that may be present in household drinking water supply systems containing leaded components. Pb exposure can affect the development of the nervous system and brain in children and cause serious health problems in adults. Worldwide, lead water crisis have been reported in Washington D.C., Flint (Michigan, USA), Scotland, and Hong Kong. The lead contamination problem in drinking water is a global public issue that has been studied for decades. While the majority of incidents were caused by lead service lines used in water supply systems, lead contamination from lead solder joints and brass fittings is becoming an emerging problem in modern cities. Water supply chains in high-rise buildings are long and torturous with distributed small-size lead sources. The lead contamination and transport processes in these premise plumbing systems are complicated. Hitherto, there is no theoretical model for predicting lead time-history at consumer taps.

This is a comprehensive study on lead contamination and transport in drinking water supply systems. The lead contamination problem is studied from three perspectives. First, a 3D computational fluid dynamic (CFD) model is developed for Pb concentration prediction at consumer taps, where the shear flow is fully simulated to guarantee the most accurate prediction. Second, the 3D model is extended into a 1D-3D coupling model for predicting lead concentration in random daytime (RDT) samples by performing a large number of fluid dynamic calculations under the Monte Carlo simulation framework. Finally, a theory of galvanic corrosion prediction in drinking water environments is proposed. These works offer a comprehensive overview of lead contamination and transportation in drinking water supply systems.

Based on the equilibrium concentration approach and the 3D CFD model, the time course of lead concentration at consumer taps is predicted. Lead release is simulated by molecular diffusion, and the shear pipe flow is fully simulated when the tap is opened. For the first time, a 3D CFD model has been used to predict lead contamination in drinking water. The predicted results agree well with the measurement data. It is the first time a complete time history of Pb contamination at consumer taps is available. Under the Monte-Carlo simulation framework, a 3D-1D coupling model is developed to predict the stochastic variation of Pb concentration in RDT samples. A large number of simulations are performed using random sample time, inter-use time, and flushing time. The computations are performed in: (i) a real-life lead soldered water supply chain; and (ii) a synthetic copper water supply chain with brass fixtures. The predicted range and distribution of concentration in RDT samples are in broad agreement with a three-year field data set (2017-2020) of the Hong Kong Water Supplies Department.

On the basis of basic electrochemical principles, a prediction model for galvanic corrosion is developed. According to Faraday’s law, the corrosion rate is related to electric current at the metal surface, and Ohm’s law describes the relationship between electric current and potential. The electric field and mass transport process are coupled to simulate the corrosion process dynamically. The parameters used at plumbing component surfaces are measured in tap water by the polarization method. The model is successfully applied to predict corrosion of three cases in water supply systems: (i) pure copper pipe; (ii) a lead soldered pipe section; and (iii) a pipe section with a brass valve in the middle. The predicted results are in good agreement with measurement data. The model explains well the rapid corrosion rate at the beginning and the linear increase of metal concentrations in water thereafter. Based on basic electrochemical principles, this model can be applied to predict corrosion in water supply systems.