Water: Its Properties, Distribution, and Significance

Water, a chemical compound, exists in nature in three physical states: liquid, gas, and solids, and all these forms are useful to human beings. Water has become a widespread life-sustaining substance, comprising 50–90% of living materials and covering nearly three-fourths of the Earth’s surface. All living organisms are composed mainly of water, the prime medium of life on earth and those of rivers are partly or wholly immersed in water. Life evolved in water, with water, and with the physical and chemical characters of natural water, and this balance is necessary. The global distribution of water is irregular. Some regions have plenty and others have shortages. The availability of liquid water depends on a reserve of inland waters, characterized by waters in lakes, rivers, reservoirs, wetlands, and groundwater. Water like other substances, expands when frozen, and help ice to float on the surfaces of the freshwater bodies. Cohesion of internal molecular constituents gives rise to another physical property of water, surface tension, which allows water organisms to traverse on the surface of the water. Water being the most essential and integral part of the lives and livelihoods of human beings for food, health, energy, and environment needs proper management in order to achieve sustainable eco-development. The water being a renewable natural resource will never “run out” the availability and variability of water impose the greatest impact on all-round development of a nation. Almost all rivers from a large country like India along with several other regions of the world have been identified as water-stressed rivers because of cumulative impacts of water abstractions, and environmental perturbations out of deforestation, global climatic changes, etc. Although life originated in water, it is really challenging for the aquatic organisms to adjust and survive in the ever-changing aquatic realm which appears to be not only unstable but hostile too as this aquatic environment is governed by unfamiliar rules of cold, wave-swept seacoasts, torrential mountain streams, and rivers, also by the very turbulent waters at the confluence of rivers with the sea. The living organisms of aquatic environments and their bioecological activities are very dependent on the prevailing ecological factors, both living and nonliving in the temporal and spatial scales. The unique physical and chemical characteristics of water and their interaction define the different aquatic environments and constrain the evolution of organisms that inhabit them.