In 2008, the world entered the “urban millennium”, with over half of the world’s population living in cities for the first time in human history. According to WHO/UNICEF’s Joint Monitoring Programme, 141 million urban dwellers worldwide lack access to improved drinking water, and one out of four city residents, 794 million in total, do not have access to improved sanitation facilities. A key Millennium Development Goal is to reduce by half those without access to sustainable safe water and basic sanitation by 2015. This is why World Water Day 2011 focuses on Water for Cities: Responding to the Urban Challenge, in the hope that concentrating international attention on these basic service challenges will encourage central and local governments, non-governmental and civic organizations, the private sector, and individuals to work in concert to actively address and overcome these challenges.