Mumbai ranks below average overall in the Index. Its best performances are in the categories of energy and CO2, land use and buildings, and water, where it ranks average. Regarding energy, the city has relatively low levels of CO2 emissions, and has embraced sources of renewable energy for electricity production, particularly hydro power. In the water category, Mumbai benefits from a relatively low level of water leakages, and it is second best for this indicator among cities with a similarly low income in the Index (under US$10,000 in per capita GDP). The city, however, ranks below average in several other categories: transport, waste, sanitation and environmental governance. Air quality is a particular challenge, with Mumbai registering a well below average result in this category. This is due mainly to very high levels of the three air pollutants measured in the Index.