Today, New Caledonia’s drinking water supply comes from the freshwater lens on the Loyalty Islands, from surface water on the east coast, and from alluvial groundwater at the base of the massifs, and especially peridotites, on the west coast. On Grande Terre (the main island), drinking water comes mainly from surface water, which is the most vulnerable to pollution, floods and droughts. Yet, of the approximately 500 catchments for drinking water, 31% distribute untreated water and only 54% of catchments have a protection perimeter (New Caledonia, 2019). Moreover, the current standards concerning the quality of water intended for human consumption were set by amended order no. 79-153 of 3 April 1979 which retains, for 15 referenced parameters, limits that are mostly higher than those defined by the metropolitan regulations and the World Health Organization (WHO). In this context, this chapter presents the data available on water quality in New Caledonia. It describes the complex dynamics between natural factors (geology, hydrology) and human factor (mining, agriculture, urban space). It underlines the diverse range of challenges related to water quality especially the natural high level of heavy metals. The presence of metals (nickel, cobalt, chromium, iron, manganese) in sometimes high concentrations in the Caledonian natural environment (soils and subsoils) constitutes a geochemical “background noise” which can also affect drinking water and food. There are several challenges for water policy in terms of water quality, including strengthening the protection of reservoirs and rivers, and establishing a more comprehensive and dense monitoring network. Water treatment or replacement of non-compliant water is a major technical and financial challenge.