provide safe water to the many illegal settlements that were expanding on the city's periphery. In Santa Marta, water coverage improved rapidly during the first three years, going from 74 percent to 87 percent, but has stagnated since 2001 (access to sewerage followed the same pattern). In Palmira (220,000) and Girardot(100,000), full coverage was achieved for both water and sewerage. In the city of Tunja (120,000 people) both water and sewer coverage went up from 89 percent in 1996 at the start of the concession to 100 percent four years later. The company Conhydra in the department of Antioquia achieved full water coverage within a few years in the towns of Marinilla, Santafe, and Puerto Berrio (combined population 170,000) starting from levels of 80 – 90 percent. The first contract under the PME program was awarded in 2000 in Montería (350,000 people). Starting from a low 63 percent, water coverage had increased to 96 percent by 2007, catching up with the national urban average. The population with access to piped water more than doubled. The improvement in sewer coverage was more modest, up from 26 percent to around 40 percent. In Soledad (400,000 people), coverage went up from 65 percent to 84 percent for water, and from 36 percent to 73 percent for sewerage in just five years. Impact on water losses The evolution of the water losses - as measured by Non-revenue water - for the nine largest and/or oldest PPP projects shows a mixed record. Strong gains were made in Montería, Tunja, Marinilla, and Palmira, but the reduction was modest in Cartagena, Barranquilla, and Santa Marta, and no progress was achieved in Girardot or Soledad. Reductions were achieved while the average network pressure went up significantly as service continuity was reestablished, which would have increased losses if no improvements had been made in the hydraulics of the distribution networks. Impact on efficiency In the case of Cartagena, the World Bank has estimated efficiency gains by comparing the evolution of the ratio of collected revenues to operational costs (operating ratio) on the one hand to that of the average tariff level on the other hand. The operating ratio is driven essentially by two factors: the evolution of operational costs and collection rates, which are controlled by the private operator, and the evolution of the average tariff, which is exogenous. Whenever the operating ratio increases faster than the tariff, efficiency