36. Today, the great pressure on water resources is rising human populations, particularly growing concentrations in urban areas. This diagram shows the impact of expected population growth on water usage by 2025, based on the UN mid-range population projection. It uses the current rate of water use per person without taking into account possible increases in water use due to economic growth or improvements in water use efficiency. The regions most vulnerable to domestic water shortages include those where access to water is already limited, the population is growing rapidly, urban centers are spreading, and the economy is burdened by financial problems and a lack of skilled workers. Even if the world maintained the pace of the 1990s in water-supply development, this would not be enough to ensure that everyone had access to safe drinking water by the year 2025.
The impacts of climate change - including changes in temperature, precipitation and sea levels - are expected to have varying consequences for the availability of freshwater around the world. For example, changes in river runoff will affect the yields of rivers and reservoirs the recharging of groundwater supplies. An increase in the rate of evaporation will also affect water supplies and contribute to the salinisation of irrigated agricultural lands. Rising sea levels may result in saline intrusion in coastal aquifers. Current indications are that if climate change occurs gradually, the impacts by 2025 may be minor, with some countries experiencing positive impacts while most experience negative ones. Climate change impacts are projected to become increasingly strong during the decades following 2025.