Global water resources refer to the total volume of water available on Earth, spanning the oceans, ice sheets, groundwater, and surface water bodies. While the Earth holds approximately 1.386 billion cubic kilometers of water, the vast majority is saline. The management of these resources is a primary focus of the UN Sustainable Development Goal 6 (SDG 6: Clean Water and Sanitation).
Classification by Salinity and Accessibility
Water resources are primarily divided based on their chemical composition and their physical state, which determines their utility for human consumption and agriculture.
| Resource Category | Percentage of Total | Availability/Status |
| Oceanic Water | 97.2% | Saline; requires desalination for human use. |
| Glaciers & Ice | 2.1% | Freshwater; mostly locked in Antarctica and Greenland. |
| Groundwater | 0.61% | Freshwater; accessible but prone to over-exploitation. |
| Surface Water | 0.02% | Includes lakes, rivers, and reservoirs; highly accessible. |
Major Freshwater Reservoirs
Freshwater constitutes only 2.5% to 2.8% of global water. Its distribution is highly concentrated in specific geographical features.
The Cryosphere (Ice and Snow)
The cryosphere holds nearly 68.7% of all freshwater. The Antarctic Ice Sheet alone contains about 90% of the world’s ice mass and 70% of its freshwater. The melting of these resources due to global warming is a significant contributor to sea-level rise.
Groundwater Systems
Groundwater is the largest store of liquid freshwater. It exists in aquifers, which are geological formations of permeable rock or sediment. In arid and semi-arid regions, groundwater provides up to 100% of the water used for daily needs.
Surface Water Bodies
Rivers and lakes, though representing a tiny fraction of the total water, are the most vital for human civilization.
- Lake Baikal (Russia): The world’s deepest and oldest freshwater lake, containing roughly 20% of the world’s surface freshwater.
- The Amazon River: The largest river by discharge, accounting for nearly 20% of the global riverine discharge into oceans.
Geographical Disparity in Water Resources
Water is not distributed equally across continents, leading to the concepts of Physical Water Scarcity and Economic Water Scarcity.
- Water-Rich Regions: Countries like Brazil, Russia, Canada, Indonesia, and China hold a significant portion of the world’s renewable freshwater.
- Water-Scarce Regions: The Middle East and North Africa (MENA) region is the most water-stressed in the world, with many countries falling below the “absolute water scarcity” threshold of 500 cubic meters per capita per year.
Emerging Trends and Challenges
The “Third Pole”
The Hindu Kush-Himalayan (HKH) region is known as the “Third Pole” because it contains the largest permanent ice cover outside the North and South Poles. It provides the perennial flow for major Asian rivers, including the Ganga, Indus, Brahmaputra, Yangtze, and Mekong, supporting over 1.9 billion people.
Virtual Water and Water Footprint
- Virtual Water: The volume of freshwater used in the production of a product, measured at the place where the product was actually produced.
- India’s Status: India is one of the largest exporters of virtual water globally due to the export of water-intensive crops like basmati rice and sugarcane.
Desalination and Non-Conventional Sources
As freshwater stress increases, nations are turning to:
- Desalination: Converting seawater to freshwater (widely used in Israel, Saudi Arabia, and UAE).
- Wastewater Recycling: Direct potable reuse of treated water (pioneered by Singapore’s NEWater).
Important Facts for UPSC Prelims
- Fossil Water: Also known as paleowater, this is groundwater that has remained in an aquifer for thousands or millions of years. The Nubian Sandstone Aquifer System in Africa is the largest known fossil water carrier.
- Water Stress vs. Water Scarcity: Water stress is defined as an annual water supply below 1,700 cubic meters per person, while water scarcity is below 1,000 cubic meters per person.
- Global Precipitation: Approximately 505,000 cubic km of water falls as precipitation each year, with 78% of it falling over the oceans.
- UN Water: The United Nations mechanism that coordinates the efforts of UN entities and international organizations working on water and sanitation issues.