Global Water Distribution and Availability

A watery planet does not mean unlimited fresh water

Only about 3% of Earth's water is fresh water; approximately 97% is saline water, mainly in seas and oceans. Seawater contains too much dissolved salt for most everyday uses without treatment to remove it.

Even fresh water is not automatically available to people. Its location, physical state and quality matter. Water frozen in a glacier cannot be used as readily as water flowing through a nearby river, while fresh river water may still need treatment before it is safe to drink.

Where fresh water is stored

Fresh water occupies several different stores. Surface water is held in rivers and lakes. These can be accessible sources, but they contain only a limited part of Earth's fresh water.

Groundwater is stored beneath the ground. An aquifer is a layer of permeable rock that holds groundwater and allows it to move through spaces or cracks. Groundwater can be reached using wells or boreholes, so access requires suitable equipment rather than simply being close to a surface water source.

Fresh water is also stored as ice in glaciers and ice caps. A small amount occurs in the atmosphere as water vapour and cloud droplets. Atmospheric water is important because precipitation transfers water back to the land, replenishing surface and underground stores.

The distinction is between water that exists and water that people can use. A store may be distant, frozen, difficult to reach or unsuitable for drinking without treatment.

Global scale: contrasts between countries and regions

Fresh water is unevenly distributed across the world. Canada, Iceland and Norway have high freshwater availability per person, whereas North Africa, the Middle East and India have much lower availability.

Climate helps explain these contrasts. Rainfall replenishes water stores, while evaporation removes water from the surface. Wetter conditions generally provide more water; dry conditions provide less. Cooler temperatures also reduce evaporation, helping water remain in stores.

Availability per person depends on population as well as the amount of water. Canada has approximately 7% of the world's renewable fresh water, but only about 0.5% of the global population. Its water resources are therefore large relative to its population. A country with considerable water resources can still have much less available per person if those resources are shared among many people.

National scale: differences within England

A national average can conceal major regional differences. In England, the amount of water available for new abstraction varies between catchments. A catchment is the area of land drained by a river and its tributaries.

During low river flows, nearly all catchments in the South East and East, and large parts of the Midlands, cannot support new abstractions because insufficient water is available. Some catchments in the South West, North and Midlands may have water available. At higher flows, more catchments have water available, although many in the South East and East remain limited.

This does not mean that homes in those regions have no tap water. It means that additional water cannot necessarily be taken from the natural environment. Existing users must be protected, and enough water must remain to support rivers and their ecosystems.

Local scale: access depends on the particular place

Within a region, availability can differ between individual rivers, aquifers and communities. Local conditions determine whether water can actually be accessed reliably and safely. These include the presence of a water source, groundwater conditions, water quality and treatment infrastructure.

Consider a comparison: two nearby communities receive similar rainfall. One has access to an aquifer, pumping equipment and water treatment; the other has limited equipment and depends on a river whose flow falls during dry periods. Similar rainfall does not give them equally reliable usable supplies.

Local checks also matter when taking water from the environment. A regional assessment may indicate that water is potentially available, but taking it from a particular location could harm nearby users or reduce river flows too far. Water availability therefore needs to be understood at all three scales, not inferred from a national total alone.