Each cell in a living organism is made up of almost 75\% water, and this allows the cell to function normally. In fact, most of the chemical reactions that occur in life, involve substances that are dissolved in water. Without water, cells would not be able to carry out their normal functions, and life could not exist.
The hydrosphere provides an important place for many animals and plants to live.Humans use water in a number of ways. Drinking water is obviously very important, but water is also used domestically (e.g. washing and cleaning) and in industry. Water can also be used to generate electricity through hydropower.}
The Hydrologic Cycle
The hydrologic cycle, also known as the water cycle, describes how all the water in the hydrosphere continually moves between oceans, lakes, rivers, land and atmosphere. During the course of the water cycle, water changes state from liquid to gas and back to liquid. The energy that drives the hydrologic cycle comes from the sun. The steps in the water cycle are evaporation, condensation, precipitation and runoff. Transpiration is an additional element in the water cycle.
- Evaporation is the process by which water on the surface changes from a liquid to a gas state, water vapor. Energy is required for evaporation to take place.
- Condensation occurs when water vapor in the atmosphere cools and collects into water droplets, forming clouds. The water loses energy when it condenses.
- Precipitation consists of rain, hail, sleet or snow falling from clouds back to Earth's surface.
- Runoff is water from precipitation that flows over the surface into rivers or streams, eventually returning to the ocean.
- Transpiration happens when water vapor returns to the air from the leaves of plants.
Water is our lifeline that bathes us and feeds us. In ancient cultures water represented the very essence of life. The Romans were the first to pipe water into their growing cities, especially with their aqueducts. They also realized that sewage water could cause damage to their people, and needed to be removed from large areas of people.
Water has played a role not only in the history of countries, but in religion, mythology, and art. Water in many religions cleanses the soul through holy water. For example, the water at Lourdes, France is thought by many religions to be sacred water with healing powers. In Egyptian mythology, the Nu was the beginning of everything and represented water. It brought life to their people, but in drought, produced chaos.
Water has always been perceived as a gift from the gods as it rained from the heavens
