Given the rising concerns over scarce energy resources and global climate change, life-cycle inventories focusing on energy use and greenhouse gas ͑GHG͒ emissions were developed for the City of Toronto municipal water treatment system ͑WTS͒. Three processes within the facility use phase of the life cycle were considered: Chemical production, transportation of materials, and water treatment plant operation. The impacts of chemical manufacturing were estimated using the economic input-output life-cycle assessment model, while the inventories for transportation and operational environmental effects were based on data from the GHGenius model and regionally averaged data. Operational burdens, 60% of which are attributed to on-site pumping, accounted for 94% of total energy use and 90% of GHG emissions. By contrast, transportation-related energy use and emissions were deemed insignificant. The normalized energy use of the studied WTS was found to be between 2.3 and 2.5 MJ/ m 3 of water treated. Water conservation practices are recommended as abatement strategies for the energy use and GHG emissions associated with water treatment. The limitations and uncertainties introduced by selected model parameters and through combining various estimation methodologies are discussed, as is the model's relevance.

Motivated by the desire to understand the impact of water supply systems on the environment, a life cycle-based hybrid methodology is used to assess the performance of two conservation scenarios, water efficiency, and rainwater harvesting, relative to the base case. The analysis carried out for the City of Toronto's residential sector estimates the operational energy use and GHG emissions, and the embodied burdens associated with water-efficient devices and rainwater tanks. Hydraulic simulations, performed on a hypothetical network to expose the impact of demand peak factor on pressure distribution at nodes, revealed some of the rainwater scenario strengths such as hydraulic stress curtailment and capital investment postponement. While both strategies led to significant water savings, the associated energy expenditures and emissions varied with the selection of system boundaries. Nevertheless, both conservation strategies are worthwhile pursuing for rendering the existing water systems more sustainable.