Abstract
Demand variations over time affect the hydraulic and water quality behavior of water distribution systems. Therefore, it is important to assess the network performance under various future water demand scenarios to plan effectively for demand management strategies, considering the network’s topology, volume, and operational conditions. The performance of a full-scale water distribution system is evaluated by means of hydraulic and water quality simulations under different hypothetical demand management strategies. Residential and nonresidential consumptions are varied, resulting in different global multiplicative factors (from 0.53 to 1.18). Criteria including water loss, velocity, water age, free chlorine, and THMs are selected to compare the performance of the network between the current scenario and eight demand scenarios. Water conservation generally increases nodal water age values more in smaller diameter pipes. A nodal chlorine residual reliability index is proposed to account for the duration of low chlorine residuals. With a goal of maintaining a reference free chlorine concentration of ≥0.2 mg/L, the reliability index is less than 0.9 for about 14% of nodes under the reference scenario and this proportion increases to 34% of nodes under the most extreme future water conservation scenario. The robustness of the studied network under different water conservation scenarios is tested by increasing the chlorine residual at the outlet of the WTPs from 1 to 2 mg/L. This is an easily implemented adjustment and dramatically improves the chlorine reliability (<0.9 at only 15% of the nodes), even for the most extreme future water conservation scenario. However, this reliability comes at the cost of higher yet compliant THM concentrations for the low demand scenarios, revealing the challenges of balancing competing water quality goals. With a goal of maintaining a reference level of THMs at ≤80 ug/L, the THM reliability index is ≥0.9 at almost all nodes even under the most extreme conservation scenario. The evaluation of self-cleaning potential velocities shows that sufficient velocities can only be reached at daily maximum flow in 5% of smaller diameter piping even in the reference scenario.
Highlights
Water conservation measures are being implemented around the world in response to constraints such as water scarcity and drought stress conditions or to reduce the cost and energy associated with drinking water treatment and distribution
The nodal water age values as well as the differences between median water ages under different scenarios got smaller for groups of nodes with a larger diameter
The results indicated clearly that water quality generally deteriorated as the total water consumption decreased, and the increased water age resulted in l1o2wofe1r8 chlorine residuals and higher THM levels across the system
Summary
Water conservation measures are being implemented around the world in response to constraints such as water scarcity and drought stress conditions or to reduce the cost and energy associated with drinking water treatment and distribution (pumping). As water conservation can adversely affect the water quality, the impacts of future water conservation strategies on the robustness of water networks should be considered to adapt their operation and design, as well as to define demand management policies. Water consumption reduction has been mandated by existing codes and standards such as the U.S Environmental Protection Agency’s WaterSense program, and it is possible that the use be reduced even more in the future [1]. Meteorological variables, the spatial shifts in population and densification, installation of meters and smart meters, water volume pricing, and adoption of water-efficient appliances are among the factors that can affect household water demand quantification [2,3,4,5]. Water companies and utilities have observed that water use is not necessarily increased by population growth [1]
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