Why is there a need of rainwater harvesting?

Answer 1

Rainwater is a clean, inexpensive and readily available source of water. Even in desert areas, substantial amounts of rainwater are being collected, stored and used for a variety of purposes, including drinking water. Consider this: for every inch of rain that falls on one square foot of surface, a rainwater harvesting system can collect .623 gallons of water. That's 620 gallons of water for 1,000 square feet of surface area. Example: Let's say the average rainfall in a given area is 25 inches per year. A surface area of 1,000 square feet can produce 15,500 gallons of water per year. Even though the planet has a large amount of water, 97.5% of it is saline. Seventy percent of the remaining 2.5 percent is locked in the polar ice caps or in glaciers. Only .75% (three-quarters of a percent) remains as potable (drinkable) water and irrigation for agriculture. The world's population now exceeds 6 billion people. Already one-third of the population does not have adequate drinking water, much less water for agriculture. Not enought water for agriculture means that these portions of the population cannot produce enough food, further straining the world's resources, increasing famine, disease and wars over food supplies, water and more desireable land. In many parts of the world, people depended upon aquifers (underground deposits of water) for drinking, cooking, washing and irrigation needs. These aquifers do "recharge" slowly as rainwater seeps down through layers of earth and rock. Unfortunately, in much of the world, including North America and Europe, these aquifers are being drawn down faster than they can recharge. In some areas of the American southwest, many farms are already having trouble extracting water from aquifers. In some major cities (Houston, Texas, for example), the ground is sinking into collapsing aquifers. Changing from aquifers to surface water (lakes, rivers and reservoirs) has become a major theme in urban areas. In many urban areas, however, there is not even enough surface water to adequately supply the population. Desalination projects do work on a small scale, but they require massive amounts of energy. Heavy metals, along with strong saline solutions are extracted from sea water in the process. These materials need to be disposed of in ways that are not harmful to the environment. They cannot be put back into the sea because the high concentrations are lethal to sea life. Most desalination processes are injecting these poisonous materials back into the earth.