Challenges include poor quality and intermittent water supply (only 40% of those with house connections receive water continuously), the loss of storage capacity in reservoirs behind dams through siltation accelerated by erosion in the Aberdare Range, lack of access to adequate sanitation in slums where half the population of the city lives, blockages of sewers resulting in overflows, and unused capacity in the city's largest wastewater treatment plant in Dandora. Another problem is political infighting and corruption, leading to the firing of the entire Board of the Nairobi Water Company in 2009.