Water Provision

Source of Water

Worldwide, most water withdrawals are fresh water from surface or ground sources, with small amounts from treated, recycled, or desalinated water.

Source: AQUASTAT ¹.

Cost of Water Provision

Worldwide, water treatment and distribution requires 10.2 exajoules of primary energy, almost 2% of the world total consumption, and about 4% of world electricity ². The energy intensity of water may vary widely depending on how it is treated and distributed.

Sources: Gandiglio et al. ³, Inbar et al. ⁴, IRENA ⁵, Pan et al. ², Reekie ⁶, WaterReuse ⁷.

In expensive coastal water markets such as California, desalinated water can be competitive with conventional options and serve as a backstop against the risk of shortage. However, desalination makes little sense where freshwater sources are abundant.

Sources: Cooley et al. ⁸, Ghaffour et al. ⁹.

Waste Water Treatment

Most wastewater today is discarded without treatment, but in principle it can mostly be recycled, extending freshwater resources and reducing pollution.

Sources: UN ¹⁰, Water Authority of Israel ¹¹.

In theory, the energy that can be extracted from wastewater exceeds the energy required for treatment by a factor of 5-10 ¹², and in practice, emerging technology might make wastewater recovery a net energy producer ¹². Electricity, biogas, hydrogen, and nutrients can potentially be extracted from wastewater ¹².

The United States treats about 47 km3 wastewater per year, which, if fully recycled, would supply about 10% of total water withdrawal ¹³.

Desalination

Desalination is currently a niche but rapidly growing source of water ¹⁰.

Desalination has several significant environmental impacts. Aquatic organisms are entrapped or entrained by the intake or processing equipment. Additionally, discharge of the highly saline brine, which may be mixed with harmful chemicals and heavy metals, harms marine life ¹⁴.

Based on studies of power plants in California with once-through cooling, it is estimated that a desalination plant in California, which produces 50 million gallons (189,000 cubic meters) of fresh water per day from 110 million gallons (416,000 cubic meters) of sea water intake, impinges 2 pounds (0.9 kilograms) per day of marine life ¹⁵. By comparison, a pelican takes in up to 4 pounds per day of food ¹⁵. The same plant has an entrainment impact of about 235 million fish larvae per year, the equivalent of five adult halibut fish per year ¹⁵. If California were to procure its entire water supply of 95 billion cubic meters ¹⁶ from desalination, 1,378 such plants would be required, with an impingement impact of 1250 kilograms per day of marine life and an entrainment impact equivalent to 6,500 adult halibut fish.

Desalination also creates brine as a waste product and is energy intensive. ¹⁷ Despite these negative externalities, desalination can provide the most economic and eco-friendly method for producing freshwater in use cases where the alternatives are worse. One such use case are small, semi-arid islands with limited aquafers or rainfall such as those found in the Aegean Sea.

Rainwater Capture

Better use of captured rainwater can mitigate the need for irrigation, costly treatment, groundwater depletion, or desalination. It is estimated that rainwater harvesting could reduce the world need for water withdrawal by 500 km3 per year ¹⁸, or a bit over 10% of current withdrawal, though the economic potential is uncertain.

Atmospheric Water Generation

Even in deserts, the atmosphere contains water vapor that can, in principle, be collected as potable water. The energy requirements have been estimated at 300-650 kWh/m3 ⁴, perhaps suitable for drinking water where there are no other options, but prohibitive to supply water on a large scale.