A general water supply planning model: Evaluation of decentralized treatment

Increasing population, diminishing supplies and variable climatic conditions can cause difficulties in meeting water demands; especially in arid regions where water resources are limited. Given the complexity of the system and the interactions among users and supplies, a large-scale water supply management model can be useful for decision makers to plan water management strategies to cope with future water demand changes. It can also assist in deriving agreement between competing water needs, consensus and buy-in among users of a proposed longterm water supply plans. The objective of this paper is to present such a general water supply planning tool that is comprised of modular components including water sources, users, recharge facilities, and water and wastewater treatment plants. The model is developed in a system dynamics simulation environment that helps users easily understand the model structure. The model was applied to a realistic hypothetical system and simulated several possible 20-year planning scenarios. In addition to water balances and water quality analyses, construction and operation and maintenance of system components costs were estimated for each scenario. One set of results demonstrates that construction of small-cluster decentralized wastewater treatment system could be more economical than a centralized plant when communities are spatially scattered or located at steep areas where pumping costs may be prohibitive.