Collection refers to the process by which water gathers back into bodies of water such as rivers, lakes and oceans. This begins with precipitation, when water falls from the clouds in the form of rain, snow, sleet or hail. A lot of the time, precipitation falls directly into a body of water, but at other times, it soaks into the ground, where plants, people and animals end up drinking it as ground water. Most of the water will end up leaching back into bodies of water through the soil.
According to Shoalhaven Water, the total water supply on the Earth is about 13.7 billion cubic kilometers, but the vast majority of it (about 97 percent) is oceanic salt water, while the rest is fresh water. Because it is not possible to consume salt water, and because desalinization is both time-consuming and costly, it is important for humanity to maintain a clean supply of fresh drinking water. Current farming and consumption practices are placing much of the fresh water supply at risk. One example is the Ogallala Aquifer, which sits under much of the American Midwest. Irrigation by farmers in the Midwest is draining this aquifer, which could take as long as 6,000 years to refill, according to Mother Earth News, as no one has discovered a way to hasten the collection process.