Comparative life cycle assessment of three alternative techniques for increasing potable water supply in cities in the Global South

Clean water is becoming an increasingly scarce resource, and its availability is already compromised in many cities. Several techniques for increasing urban water availability are under consideration, but how their life cycle environmental impacts compare amongst one other remain largely unknown. For cities in developing countries, which are more susceptive to water shortages, this is particularly true. Furthermore, to directly compare these technologies, they must be evaluated using the same methodological framework. This paper compares, for the first time, the life cycle environmental impacts of the following three techniques: i) seawater desalination by reverse osmosis (SWRO); ii) indirect potable wastewater reuse (IPR) through an upflow anaerobic sludge blanket digestion reactor, oxidation ditch, ozonation, and managed aquifer recharge; and iii) rainwater harvesting (RWH) to substitute drinking water from the local distribution network. These techniques were evaluated in the Brazilian southern city of Florianópolis. Life cycle assessment (LCA) was used to calculate 15 environmental impact categories with the ReCiPe methodology. Variations in electricity consumption according to technical developments, effluent quality, and pumping efficiency were taken into consideration with parametric analysis. Furthermore, a sensitivity analysis was carried out regarding the direct emissions of methane and nitrous oxide during IPR, and the electricity mix. SWRO indicates the highest results for 12 out of the 15 impact categories, and IPR indicates the lowest values in nine categories. Electricity consumption is the main contributor to most impact categories during SWRO and IPR. Out of six categories (including climate change and human toxicity), RWH is the preferable option whilst comparatively also presenting the worst results for water depletion and marine eutrophication, with glass fibre produced for storage tanks being the main contributor. In the climate change potential category, for instance, SWRO, IPR and RWH have mean results of 751, 998, and 591 kg CO2 eq./1,000 m3, respectively. However, the sensitivity analysis showed that if direct emissions of CH4 and N2O in IPR are low, then the IPR technique will have better results than the SWRO method, resulting in 710 kg CO2 eq./1,000 m3. Additionally, the country electricity mix was found to be highly influential in the environmental impacts, especially for SWRO and IPR. The results obtained from this research will inform stakeholders, particularly those in developing countries, about possibilities of adopting new techniques for increasing water supplies, without comprising the environmental sustainability of these systems.