water

Despite its complex role in life and the ecosystem, water’s chemical makeup is quite elementary: H₂O. Its structure is simple, symmetric, and non-linear.

The hydrologic cycle includes major fluxes and volumes of water. Earth has an abundance of water, but the purity, salinity, and availability differ greatly over time and place.

Nearly 4.8 billion people, or 80% of the world’s population in 2000, reside in areas with significant water security or biodiversity threats. Because of the critical relationship between water and life, improving water quality is clearly a significant way to improve public health worldwide.

Several demographic factors around the world affect water use: population, urbanization, standards of living, prevailing mix of economic sectors, and number of households.

Water use for agriculture and industry gets embedded into different products and services. In some cases, the water embedded in those goods is significant enough to be tracked. This embedded water, or virtual water, is often known as the “water footprint.”

Three separate but important water events—an oil spill, a burning river, and a trip to the moon—spurred the modern environmental movement and its attentiveness to protecting water.

The old seaman’s ditty “water, water everywhere, nor any drop to drink” from The Rime of the Ancient Mariner by Samuel Taylor Coleridge captures the essence of being surrounded by seawater unsuitable for consumption.

Keeping track of water is done through a scientific accounting methodology known as the Reynolds transport theorem, which is used to track the flows, fluxes, and storage of water in a physical system.

Rainfall varies from less than 4 inches (100 mm) to greater than 160 inches (4,000 mm) per year within the contiguous United States.

The location and source of liquid water affects the usability of water as much as its salt content. Surface water sits on top of the ground in rivers and lakes or in the oceans, ultimately covering 70% of Earth’s surface.

Just as there are many different forms of energy, there are also different forms or types of water. These types differentiate the water’s composition, where it came from, and the different labels we assign them.

Water serves an important role for transportation. While railroads are more energy-efficient at moving goods than trucks, cars, or planes, many people do not realize that waterborne commerce is even more energy efficient.

In addition to the external water infrastructure—dams, canals, and reservoirs—there is also an extensive piped water infrastructure. That piped system includes the components for collecting, treating, and distributing drinking water, and for collecting, treating, and releasing treated wastewater. The network is vast, expensive, and leaky.