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This paper evaluates the financial and economic costs of reusing wastewater with reverse osmosis (R.O.) purification systems to mitigate the risks of near potable quality water shortages in an urban water system. A distributional analysis is also undertaken to identify those who bear the externalities of the system. A rich data set is available to conduct an ex-post analysis of such a system operating in Cyprus for several years. The levelized financial cost of the R.O. system if it operates at a 75% utilization rate is USD 1.18/m3, while the levelized economic cost that includes all the externality impacts is USD 1.20/m3. However, the closeness of these two values hides a large set of externalities that affect different groups in society in disparate ways. The analysis shows that reusing wastewater in conjunction with a system of R.O. is a very effective way to mitigate the risks of water shortages in a more extensive water system. It also highlights the importance of the nature of the electricity system that generates the electricity to power the R.O. plant in determining the ultimate economic cost of reusing wastewater.

One of the most effective strategies to mitigate water shortages worldwide is to reuse treated wastewater for freshwater production employing reverse osmosis (RO) technology. This strategy is appropriate in urban areas of arid or semi-arid regions as it can provide a sustainable and reliable water source close to the consumers. One of the drawbacks of RO is the high variability of production costs due to the electricity intensity. In addition, depending on the electricity source, it can also result in substantial environmental costs. This study showed that upgrading pumping and RO membrane systems of a wastewater reuse plant in Cyprus can significantly alleviate these drawbacks in terms cost, water recovery rate, and air pollution. The water-recovery rate of the upgraded RO plant increased from 43.2 to 75 percent, which resulted in a substantial net financial benefit due to the reduction in the quantity of wastewater purchased and the increase in potable water produced. The upgraded system also reduced the electricity requirement from 3.63 kWh/m3 to 1.92 kWh/m3. Pollution emissions decreased substantially because of the reduction in electricity requirements. The beneficiaries of these lower emission costs are the residents of Cyprus and global society. Overall, the benefit of upgrading the plant is highly attractive with more than 65 percent annual real internal rates of return in financial and economic terms. Positive net present values are realized for all the scenarios considered.