The water cycle, along with the carbon cycle, is an essential requirement for every form of life. Water is present within the cells of our bodies, and even at this level it is in perpetual motion. It is water that gives the cell its volume, allows it to breathe, and to obtain nourishment. This simple molecule is needed by everything that lives. The living water cycle is repeated again and again, not just within each plant or animal, but on a planetary scale.
Among these constant changes, there is a visible circulation of water in the form of clouds and rain, the water that fills springs, feeds wells, runs into rivers, and rejoins the oceans of the world. This is called blue water. But water can also be invisible to human eyes, in the form of evaporation from the surface of oceans and land, and plant transpiration from the surfaces of leaves. This is called green water because it creates biomass. The water cycle and the carbon cycle come together inside the living tissues of plants. Here this interdependence is complete, because it is water that erodes rocks, allowing plants to obtain the minerals they need.
It is not the case that water is running out. Unlike oil, water is not destroyed when it is consumed. But we are disturbing its natural cycle. For example, the deforestation of huge areas of land has doubled the quantity of blue water¬—water that flows through streams and rivers and ultimately empties into the oceans. We have thereby altered the frequency and intensity of rainfall, mostly with the effect of making the air drier. But what we have done can still be undone. For example, on J. David Bamberger’s 5,500-acre (2,220-hectare) ranch in Texas, there was formerly no water and no usable pasture. After the replanting of native grasses that had disappeared through overgrazing, dry springs and streams began to flow once again, creating enough water to run the ranch and several households in the area.