Water quantity and quality (particularly in relation to pollution by pesticides and fertilisers) are essential parameters for the functioning of all ecosystems. The competing and potentially conflicting demands of this limited resource from different sectors, make water policy highly strategic to the conservation and sustainable use of biodiversity. Wetlands also have outstanding importance for the conservation and sustainable use of biodiversity, as recognised in the Ramsar Convention.
Natural vegetation cover in water catchments helps to maintain hydrological cycles, regulating and stabilising water runoff, and acting as a buffer against extreme events such as flood and drought. Vegetation removal results in siltation of catchment waterways, loss of water yield and quality, and degradation of aquatic habitat, among other things. Vegetation also helps to regulate underground water tables, preventing dryland salinity which affects vast areas of agricultural lands, at great cost to the community. Wetlands and forests act as water purifying systems, while mangroves trap silt, reducing impacts on marine ecosystems.