The Republic of Zambia gained its independence from the United Kingdom in 1964 and has been a multiparty democracy since 1991. The country, with its capital Lusaka, is landlocked in the southern part of Africa. It is home to 11.5 million people from more than 70 ethnic groups and its official language is English. Zambia is among the world's least developed countries and faces steep challenges from poverty and AIDS. In 2007 some 14 per cent of women and men between the ages of 15 and 50 tested positive for HIV. Although Zambia is a country with sufficient water, the quality of both its surface and ground water is decreasing owing to industrial and agricultural pollutants, extensive mining activities, but also to a lack of latrines. Only 59 per cent of households have access to safe water. Water- and sanitation-related diseases such as malaria and diarrhoea are therefore the cause of major health problems in Zambia; malaria takes its toll on the population with nearly four million clinical cases and 50,000 deaths per year.