Water covers over 70% of the Earth’s surface, but only a tiny fraction of it is freshwater available for human use. The vast majority is locked up in glaciers, ice caps, and deep underground. With a growing global population and rising water consumption per capita, there are legitimate concerns over whether we may one day face a global water shortage. So just how much usable freshwater is left? Let’s take a look at the numbers.
Total Global Water
The total amount of water on Earth is about 1.386 billion cubic kilometers. This includes all the water in oceans, lakes, rivers, groundwater, glaciers, ice caps, and atmosphere.
Oceans contain the vast majority of Earth’s water, accounting for about 96.5% of the total global water volume. This equates to about 1.335 billion cubic kilometers of ocean water.
| Water Source | Volume (km3) |
|---|---|
| Oceans | 1,335,000,000 |
| Ice caps and glaciers | 29,000,000 |
| Groundwater | 5,614,000 |
| Freshwater lakes | 91,000 |
| Soil moisture | 16,500 |
| Atmosphere | 12,900 |
| Rivers | 1,250 |
| Biosphere | 1,120 |
| Total global water | 1,386,000,000 |
After oceans, ice caps and glaciers contain the next largest share of global water – around 29 million cubic km. Then comes groundwater, lakes, soil moisture, atmosphere, rivers, and water contained within living things.
Freshwater Availability
While the total volume of water on Earth is vast, only a small portion of it is freshwater that is actually accessible and usable.
Oceans are too salty for most uses, including drinking, agriculture, and industry. And the water locked up in glaciers, ice caps, atmosphere, and ground deeper than we can drill isn’t viable to extract.
The most readily available and renewable freshwater comes from lakes, rivers and shallow groundwater. These sources account for only about 0.3% of total global water.
| Freshwater Source | Volume (km3) | Percent of Total Freshwater |
|---|---|---|
| Groundwater | 10,530,000 | 30.2% |
| Glaciers and ice caps | 24,064,000 | 68.7% |
| Surface water (lakes, rivers, swamps) | 91,000 | 0.26% |
| Soil moisture | 16,500 | 0.05% |
| Atmosphere | 12,900 | 0.04% |
| Biosphere | 1,120 | 0.003% |
| Total global freshwater | 34,715,520 | 100% |
While fresh groundwater accounts for about 30% of total freshwater reserves globally, much of it is deep underground and not renewable on human timescales.
The most accessible freshwater for human use equates to around 0.5% of total global water, found in lakes, rivers, soil moisture and some shallow groundwater supplies.
Water Scarcity Concerns
So how much usable freshwater is there really for a growing human population?
Concerns over water scarcity are focused on the limited supplies of renewable freshwater: surface water in lakes/rivers and shallow groundwater that is replenished by rain.
Based on data from the UN and other agencies, global renewable freshwater supplies are estimated at:
– Lakes & Rivers: 91,000 km3
– Shallow Groundwater: 10,530 km3
That’s a total of around 10,621,000 km3 or 10.6 million cubic kilometers of renewable freshwater on Earth.
Factoring in water loss from evaporation and ecology, it’s estimated that about 4,200 cubic km of this is actually available for human use each year.
With the current world population of 7.9 billion, that equates to about 528,480 liters (139,699 gallons) of available freshwater per person per year.
This seems abundant compared to average water consumption today:
| Use | Average Consumption Per Capita |
|---|---|
| Domestic/Municipal | 50-300 liters per day |
| Agriculture | 500-2000 liters per day |
| Industry | 20-1700 liters per day |
However, water demand is projected to grow significantly:
– Global population may reach 8.5-10 billion by 2050
– Average water use per person is increasing with development
– Water-intensive meat demand is rising around the world
This means accessible renewable freshwater per person could decline to around 457,000 liters (121,000 gallons) per year by 2050.
Regions with lower natural water availability per capita, like Africa and the Middle East, would experience the most acute shortages. Agriculture, which consumes the bulk of freshwater globally, would also feel major impacts.
More Alarming Scarcity Projections
Some researchers warn that usable freshwater reserves may be even more limited than the above figures suggest.
Accounting for additional constraints and losses, one study estimates the global renewable freshwater accessible for human use is around 900-1200 cubic km per year, or about 153,000 liters (40,000 gallons) per person annually today.
Another estimate puts the figure at just 760 cubic km per year, or about 96,200 liters (25,400 gallons) per capita currently available for human use after ecological requirements.
By these figures, large portions of the global population may already be living under severe water scarcity conditions, defined as less than 500 cubic meters per person annually.
However, estimating accessible global freshwater reserves remains challenging. There are disagreements among experts on quantities, recharge rates, overlap between groundwater and surface water, and how much can be sustainably withdrawn from underground aquifers.
But most agree that water demand appears on course to outstrip easily available supplies in many parts of the world by 2050 without major conservation and efficiency measures.
Desalination Potential
With concerns over depleted freshwater supplies, desalination of seawater is increasingly being used and proposed as a solution.
Desalination is energy-intensive and expensive, currently costing $0.50 to $2 per cubic meter. The world’s approximately 16,000 desal plants provide less than 1% of global water needs.
But the potential supply is essentially unlimited. The oceans contain 97% of all water on Earth. Even assuming 10% efficiency, desalination could in theory expand freshwater resources by 130 times current accessible supplies.
The costs and energy requirements of desalination are constantly improving. Renewable energy sources like solar and nuclear could provide cleaner energy to power desal plants.
According to the UN, increases in desalination capacity of 10-20% annually are already occurring in water-stressed regions. It is among the supply and conservation solutions likely needed to meet rising long-term water demand.
Water Conservation
While expanded desalination can provide a new water source, conserving existing freshwater is perhaps the most important solution.
Some major opportunities for improved water conservation include:
– **Agricultural efficiency** – Irrigation consumes around 70% of water worldwide. Improving the efficiency of agricultural water use through methods like drip irrigation, rainwater harvesting and advanced moisture sensors can significantly reduce demand.
– **Leak reduction** – Developing countries lose up to 50% of drinking water to pipeline leaks. Repairing these could save substantial volumes.
– **Water reuse** – Using recycled wastewater for purposes like irrigation and industry can conserve water supplies. Israel reuse 80% of its waste water.
– **Consumer education** – Encouraging simple conservation habits like taking shorter showers, fixing leaks, and reducing outdoor watering can meaningfully lower household water use.
– **Regulation and pricing** – Policies requiring water-efficient technologies and practices in sectors like agriculture and landscaping are important for conservation. Appropriately pricing water to discourage waste can also help reduce excessive use.
Employing these and other conservation tactics widely has great potential to put the world on a more sustainable water management path.
Conclusion
The Earth contains a vast 1.386 billion cubic km of water, but the portion accessible and renewable for human use is far more limited.
Estimates of our globally available freshwater reserves vary, but are likely in the range of 100,000 – 500,000 liters (26,000 – 132,000 gallons) per person per year.
With the world’s population rising towards 10 billion people by 2050, and water demand growing, many regions may face chronic freshwater shortages within decades.
Wiser management of existing water through conservation and efficiency improvements in all sectors is crucial. Expanded use of desalination can also help produce new sources of freshwater where economically viable.
Carefully stewarding our finite but essential freshwater supplies will be one of the world’s most pressing challenges in the coming century. But with proactive efforts taken now to moderate demand and increase sustainable supply, severe global shortages are avoidable.
