Sustaining water. Population and the future of renewable water supplies.
This report examines the effect of population size, growth, distribution, and consumption patterns on renewable water supplies. Even though more than 66% of this planet is covered with water, fresh water makes up only 2.5% of the entire water supply and 69% of that is in the polar ice caps. These figures take on even more meaning as the population increases. The rate at which the global hydrologic cycle renews or replenishes fresh water resources determines the availability of fresh water for human use. Evaporative demand and the timing and location of precipitation contribute greatly to its availability. The greatest drain on water supplies is agriculture (69% of all use), followed by industry and energy (23%), and household use (8%). Desalination of our oceans has been hailed as a technology providing an inexhaustible water supply, but extracting salt from seawater is expensive and depends on nonrenewable, pollution-causing fossil fuels. Acute water shortages have already plagued some countries, regions, and municipalities. Europe and North America could not have industrialized had it not been for dependable sources of abundant water. Yet, many developing countries do not have such access, making economic development more difficult for them to achieve. Countries with less than 1700 cubic meters/person, less than 1000 cubic meters/person, and less than 500 cubic meters/person face water stress, chronic water scarcity, and absolute water scarcity, respectively. The number of water-scarce countries increased from 7 in 1955 to 20 in 1990, and if population growth projections continue, there will be 30-35 water-scarce countries by 2025. Deteriorating water quality caused by raw sewage and industrialized and agricultural wastes further reduces the availability of fresh water and causes numerous diseases (e.g., diarrhea). Access to potable water and sanitation is needed to achieve individual health. Water will eventually overshadow oil as a scarce and precious resource. Population stabilization, water conservation, and more efficient use of water are the most effective long-term strategies to manage water scarcity.