Water supply and sanitation in Nairobi is characterised by achievements and challenges. Among the achievements is the expansion of infrastructure to keep pace with population growth, in particular through the construction of the Thika Dam and associated water treatment plant and pipelines during the 1990s; the transformation of the municipal water department into an autonomous utility in 2003; and the more recent reduction of water losses – technically called non-revenue water – from 50 to 40%.