Aguas Argentinas, the operator of the world's biggest privatized water supply and wastewater collection system, was faced with a challenging task at the beginning of the 30-year concession; new service had to be provided to 1.6 million more people in the first 5 years. As the first step, an extensive study consisted of a flow measurement campaign and a computer model of the Buenos Aires' water distribution network was conducted during the three summer months of 1994. The purpose of the study was to: collect the missing information and evaluate the operation of the existing system; find solutions for short-term problems while developing design criteria for mid- and long-term planning; and revise and fine-tune the Water Master Plan to optimize investments.