Groundwater & Seawater
Groundwater is the largest store of accessible freshwater. Seawater desalination is increasingly used in arid regions despite high energy costs.
Most of the liquid freshwater that humans can readily use is stored underground as groundwater. Oceans hold the vast majority of Earth’s water, but it is too salty for most uses unless desalinated.
Groundwater
Groundwater fills pores and fractures in soil and rock. It supplies drinking water for billions of people and supports irrigation in many dry regions. Because it is hidden, groundwater is often over-extracted. Once depleted or contaminated, recovery can take decades or longer.
Seawater and Desalination
Desalination removes salt from seawater or brackish water, producing freshwater. Reverse osmosis is the dominant technology. Desalination is energy-intensive and can be expensive, but costs have fallen and it is a critical water source for some coastal cities and arid countries. Environmental concerns include energy use and the disposal of concentrated brine.
Balancing the Two
Sustainable water strategies often combine careful groundwater management with, where appropriate, desalination and wastewater reuse. Protecting aquifers from pollution and over-pumping remains one of the most important water challenges of our time.
Groundwater and the ocean represent two extremes of Earth’s water — one mostly hidden and finite on human timescales, the other vast but requiring energy to make usable.