- Two thirds of the Earth is covered with water. Most of this water is in oceans and seas.
- Water is essential for life.
- Water vapor gets added to air by evaporation and transpiration.
- The water in the oceans and seas has many salts dissolved in it — the water is saline. So, it is not fit for drinking and other domestic, agricultural and industrial needs.
- Water in the form of vapor goes into air by evaporation and transpiration, forms clouds, and then comes back to the ground as rain, hail or snow.
- Excessive rains may cause floods while lack of it for long periods may cause droughts
- A part of the rainwater gets absorbed by the ground and seems to disappear in the soil. Some of this water is brought back to the air by the process of evaporation and transpiration. The rest seeps into the ground. Most of this water becomes available to us as ground water. Open wells are fed by ground water. Ground water is the source for many lakes as well.
- Water brought back to the surface of the earth by rain, hail or snow, goes back to oceans. Thus, water from the ocean and surface of the earth goes into air as vapor; returns as rain, hail or snow and finally goes back to the oceans. The circulation of water in this manner is known as the water cycle.
- This circulation of water between ocean and land is a continuous process. This maintains the supply of water on land.
- Only a small fraction of water available on the Earth is fit for use of plants, animals and humans. Most of the water is in the oceans and it cannot be used directly. When the level of the ground water decreases drastically, this cannot be used any more. The total amount of water on Earth remains the same, but, the water available for use is very limited and is decreasing with over usage.
- One way of increasing the availability of water is to collect rainwater and store it for later use. Collecting rainwater in this way is called rainwater harvesting.
- Rooftop rainwater harvesting is the system in which the rainwater is collected from the rooftop to a storage tank, through pipes. This water may contain soil from the roof and need filtering before it is used. Instead of collecting rainwater in the tank, the pipes can go directly into a pit in the ground. This then seeps into the soil to recharge or refill the ground water.
- Another option is to allow water to go into the ground directly from the roadside drains that collect rainwater.
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