How Much Water Is on Earth? And Why Only 0.5% Is Drinkable

Earth has about 1.38 billion cubic kilometers of water total — around 326 million trillion gallons. Of that, 97.5% is saltwater in the oceans, and only 2.5% is freshwater. Most of the freshwater is locked in glaciers and deep groundwater, leaving just 0.5% of Earth's water in liquid form that humans can actually drink.

The full breakdown

If you imagine all of Earth's water in one bucket, here's what's in it:

• Oceans — 97.5%
• Glaciers and ice caps — 1.75%
• Groundwater — 0.74% (half of it too deep or saline)
• Lakes and rivers — 0.013%
• Atmosphere — 0.001%
• Soil moisture, biosphere — 0.001%

The drinkable portion — accessible freshwater lakes, rivers, and shallow groundwater — is about 0.5% of the total.

What 1.38 billion km³ actually looks like

If you shaped all of Earth's water into a single sphere, it would be about 1,385 km in diameter — roughly the size of Pluto's moon Charon. That looks huge floating in space, but it's tiny compared to Earth itself.

The famous USGS visualization shows this sphere next to Earth, and most people's reaction is "that's all of it?" We think of water as infinite because oceans look flat-horizon. It's not. Earth is a rock with a thin, wet skin.

Where freshwater actually sits

Of the 2.5% that's freshwater:

• 68% is locked in glaciers and the Greenland/Antarctic ice sheets.
• 30% is groundwater (aquifers, some thousands of meters deep).
• Less than 1% is in rivers and lakes combined.
• A fraction of a percent is in the atmosphere and soil.

Lake Baikal in Siberia alone contains 20% of all unfrozen surface freshwater on Earth. Drink that fact for a moment.

Where humans get water

About 69% of human freshwater use goes to agriculture, 19% to industry, and 12% to households. Of the household portion, direct drinking is a tiny fraction — most is showers, toilets, and laundry.

Urban water systems pull from 3 sources: surface water (rivers, reservoirs), aquifers (groundwater), and increasingly desalination. Desalination costs about $1 per cubic meter, which is expensive but viable for coastal cities.

The groundwater problem

Many aquifers are being drained faster than they refill. The Ogallala Aquifer under the US Great Plains has dropped 100+ feet in some areas since 1950. India pumps groundwater at roughly 2x the replenishment rate in its northern states.

This is a slow-motion crisis. Aquifers that took 10,000 years to form are being emptied in 70 years.

Does Earth lose water?

Barely. A small amount escapes the upper atmosphere (about 95 tons per year) and a small amount gets added from comet impacts. Net: effectively zero change over human timescales.

The water you're drinking has been cycling through rain, rivers, and living things for 4 billion years. Statistically, some of it passed through a dinosaur.

Water off Earth

Europa (Jupiter's moon) has an ocean beneath its ice shell estimated at 2-3x Earth's total water. Enceladus (Saturn's moon) also has an ocean. Mars has frozen and subsurface water.

The solar system has a lot of water — just not in forms we can easily reach.

More planet reads

Related: how volcanoes work, Krakatoa's roar, and what if we lived underwater.