Water is one of our most natural resources. Without it, there would be no life on earth. Hydrology has evolved as a science in response to the need to understand the complex water system of the earth and help solve water problems. This hydrology primer gives you information about water on Earth and humans’ involvement and use of water.

Hydrology is the study of water

Water is one of our most important natural resources. Without it, there would be no life on earth. The supply of water available for our use is limited by nature. Although there is plenty of water on earth, it is not always in the right place, at the right time and of the right quality. Adding to the problem is the increasing evidence that chemical wastes improperly discarded yesterday are showing up in our water supplies today. Hydrology has evolved as a science in response to the need to understand the complex water systems of the Earth and help solve water problems. Hydrologists play a vital role in finding solutions to water problems, and interesting and challenging careers are available to those who choose to study hydrology. Read more

Where is Earth’s water located and in what forms does it exist? You can see how water is distributed by viewing these bar charts. The left-side bar shows where the water on Earth exists; about 97 percent of all water is in the oceans. The middle bar shows the distribution of that three percent of all Earth’s water that is freshwater.

Picture of Earth showing if all Earth’s water (liquid, ice, freshwater, saline) was put into a sphere it would be about 860 miles (about 1,385 kilometers) in diameter. Diameter would be about the distance from Salt Lake City, Utah to Topeka, Kansas, USA.

Credit: Illustration by Jack Cook, Woods Hole Oceanographic Institution; USGS.

The majority, about 69 percent, is locked up in glaciers and icecaps, mainly in Greenland and Antarctica. You might be surprised that of the remaining freshwater, almost all of it is below your feet, as ground water. No matter where on Earth you are standing, chances are that, at some depth, the ground below you is saturated with water. Of all the freshwater on Earth, only about 0.3 percent is contained in rivers and lakes—yet rivers and lakes are not only the water we are most familiar with, it is also where most of the water we use in our everyday lives exists. Read more

No, don’t take us literally! Humans cannot drink saline water. But, saline water can be made into freshwater, which everyone needs everyday. The process is called desalination, and it is being used more and more around the world to provide people with needed freshwater.

Most of the United States has, or can gain access to, ample supplies of fresh water for drinking purposes. But, fresh water can be in short supply in some parts of the country (and world). And, as the population continues to grow, shortages of fresh water will occur more often, if only in certain locations. In some areas, salt water (from the ocean, for instance) is being turned into freshwater for drinking. Read more

Lack of safe water has significant costs to societies in terms of health costs, lost economic productivity, and human suffering. For example, 14,000 to 30,000 people die each day from water-related diseases; most of these deaths are children and elderly persons. Concerns over these losses and suffering

Access to safe and reliable local water supplies is a major challenge in many communities in developing countries. Without the benefit of piped-in supplies, many people must devote part of their day to securing water for their daily needs. In this photograph, Pakistani villagers pull drinking water from a 122-meter (400-foot) well. Read more