![]() Many hydraulic network modeling packages incorporate certain algorithms to calculate the water age at any node in the network. A simplified model of water age in tanks and reservoirs was developed in the early 1990s. These models were subsequently extended to dynamical representations that determine varying water age throughout the distribution systems. The steady traveling time models were proposed by Males et al. Numerical models give the other way to estimate the water age in water distribution systems. Some reports have shown its disadvantages, that is, the tracer chemical stability, continuous regulatory compliance, customer perceptions, lack of studies on the larger distribution systems, and high operational cost. However, it is seldom applied in water distribution networks for its disadvantage. The tracer study is useful in validating hydraulic and water quality models. This method has been applied to calculate the water age throughout the water distribution system and calibrate the water quality and hydraulic models. Tracer studies involve injecting chemical into the water distribution system for a fixed period, and sensors are set up at downstream nodes to determine the duration before the water containing the chemicals passes the monitoring stations. There are two types of tools to estimate the water age: tracer studies and numerical models. In some circumstances, these tools may be appropriate, but this is not always the case. reviewed some tools to estimate the retention time and several examples presented, they conclude that there are no low-cost, effective, and reliable ways to estimate it in any circumstances. The water age primarily depends on the water distribution system design and its demands. Water age is very important for the water quality of water distribution system. Water quality will deteriorate with the increment of retention time in the water distribution system, leading to malfunctions such as disinfection by-product formation, disinfectant decay, corrosion, taste, and odor. The model provides a low-cost and reliable solution to evaluate the water retention time. The results agree well with that from EPANET. It is verified by two virtual systems and a practical application to analyze the water distribution system of Hangzhou city, China. A simplified two-step procedure is proposed to solve this statistical model. A novel statistical model using monitoring data of residual chlorine to estimate the nodal water age in water distribution networks is put forward in the present paper. In general, the concentration of residual chlorine is linearly dependent on the water demand. The residual chlorine concentration varies with the water age. The water age fluctuates with the system demand. The water retention time in the water distribution network is an important indicator for water quality.
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