Freshwater and Groundwater

About this topic

Only about 3% of Earth's water is fresh, and most of that is locked in glaciers and ice caps; less than 1% is accessible in lakes, rivers and groundwater. Groundwater is stored in aquifers, porous rock saturated with water, with the top surface the water table, and it is tapped by wells.

Overpumping depletes aquifers faster than they refill, and pollution can contaminate them. Water scarcity affects billions. Conservation, wastewater recycling, efficient irrigation and protecting watersheds help manage supplies.

Here is a sense of proportion: if all Earth's water fitted in a 1-litre bottle, only about 30 ml would be fresh and just 0.3 ml would be easily accessible surface fresh water, about one drop. Groundwater is stored in tiny spaces in sand, gravel and rock, not in underground lakes, and flows slowly, sometimes only metres a year. The Ogallala Aquifer under the US Great Plains supplies about a third of irrigation water in the country but is being drained faster than it refills, and parts of India and the Middle East face similar issues.

Water that is pumped out can cause land to sink (subsidence), as in Mexico City or Jakarta, and near coasts it lets salt water seep into the aquifer. Springs appear where the water table meets the surface. Water in a river may be only a small share of fresh water, but it is the part most people use. Efficient drip irrigation, fixing leaks, reusing greywater and protecting wetlands all reduce pressure. A common misconception is that Earth is running out of water; the water is plentiful, but clean, accessible fresh water in the right place is limited. Also, an aquifer is not a cave.