Abstract This chapter examines the main characteristics of surface waters and groundwater deposits in Chile. The extreme variations in Chilean climate are reflected directly by huge differences in hydrological conditions, from the deserts of the north to the temperate rainforests of the south. The mountainous geomorphology, the presence of major basins, and the influence of the Pacific Ocean and the South Pole on oceanic currents and air masses, all also affect water distribution across the country. Anthropogenic demand for water resources, mostly for municipal wastewater, industry and agriculture, has created pollution problems that are currently being dealt with by application of new environmental legislation. Such problems are particularly acute in the north, where scarce water deposits, already commonly contaminated by naturally occurring metalliferous deposits, have been affected by extensive mining operations. In the centre of the country, where most of the population lives, the main challenges to a high quality water supply have been more associated with treating municipal wastewater. Further south, threats to clean water resources are often associated with effluents from cellulose plants and aquaculture. The striking variations in Chilean climate from north to south, and therefore water supply, stem mainly from geographic location, topography and atmospheric circulation. The importance of geographic location derives from the position of the country along the southwestern side of the South American continent, with a corresponding strong influence from the Pacific Ocean and the South Pole. Movements of Antarctic and Subantarctic water currents and masses of polar air affect the whole country. Similarly,