The drinking water supply system in many high rise buildings in densely populated cities consists of a complex labyrinth of copper pipes and brass fixtures (valves, meters, couplings). Lead contamination in these non-lead pipe systems can occur due to the presence of lead-soldered connections, and lead containing brass fixtures. The prediction of lead concentration characteristics of random daytime (RDT) samples in these high rise buildings has hitherto not been studied. The stochastic variation of lead concentration of RDT samples is studied by a coupling of 3-D and 1-D models and the Monte-Carlo Method. A 3-dimensional CFD model based on an equilibrium concentration ($E_0$) approach is used to simulate the leaching process from different lead sources. With the calibrated $E_0$ for different materials obtained from leaching experiments, the lead source strengths of leaded components in a water supply chain can be predicted by the 3D model as a function of stagnation time. Using the predicted distributed lead sources, the transport and mixing of lead in the turbulent pipe flow can be accurately simulated by a 1D advection–diffusion model. Using the Monte-Carlo method, a large number of simulations of consumer tap water Pb concentrations is performed using randomly sampled stagnation time, inter-use time, and flushing time. The computations are performed for two representative prototypes: (i) a full scale lead contaminated water supply chain; and (ii) a chain with only clean pipes and brass fixtures. The effect of stagnation time and flushing time before water use on tap Pb levels are investigated. The predicted range and distribution of RDT sample concentrations are validated by a three-year field data set (2017–2020) of the Hong Kong Water Supplies Department.

在人口稠密的城市中，许多高层建筑中的饮用水供应系统由复杂的铜管和黄铜固定装置（阀门、仪表、接头）组成。由于存在铅焊接连接和含铅黄铜固定装置，这些无铅管道系统中可能会发生铅污染。迄今为止，尚未研究预测这些高层建筑中随机白天 (RDT) 样本的铅浓​​度特征。通过 3-D 和 1-D 模型和蒙特卡罗方法的耦合研究 RDT 样品铅浓度的随机变化。基于平衡浓度的 3 维 CFD 模型 (${乙}_0$) 方法用于模拟不同铅源的浸出过程。随着校准${乙}_0$对于从浸出实验中获得的不同材料，供水链中含铅组件的铅源强度可以通过 3D 模型作为停滞时间的函数进行预测。使用预测的分布式铅源，可以通过一维对流-扩散模型准确模拟湍流管道中铅的传输和混合。使用蒙特卡罗方法，使用随机采样的停滞时间、互用时间和冲洗时间对消费者自来水铅浓度进行了大量模拟。计算针对两个有代表性的原型进行：(i) 全尺寸铅污染水供应链；(ii) 只有干净的管道和黄铜固定装置的链条。研究了用水前的停滞时间和冲洗时间对自来水铅含量的影响。