Today is the 25th annual observance of World Water Day, a global initiative to focus attention on the importance of freshwater. Here are five facts you should know about safe and accessible water:

1. According to the United States Geological Survey Water Science School, almost two-thirds (71 percent) of the Earth’s surface is covered in water, though only 3.5 percent is freshwater. Out of the supply of freshwater: 68.7 percent is contained in ice caps, glaciers, and permanent snow; 30.1 percent is groundwater (i.e., water found underground in the cracks and spaces in soil, sand, and rock); 0.86 percent is found in ground ice and permafrost; 0.26 percent is in lakes; 0.04 percent is in the atmosphere; 0.03 percent is in swamps; and 0.006 percent is in rivers.

2. The image below shows blue spheres representing relative amounts of Earth’s water in comparison to the size of our planet. The largest sphere, which represents all of Earth’s water—including the water found in our bodies—has a diameter of about 860 miles (the distance from Salt Lake City, Utah, to Topeka, Kansas). The blue sphere over Kentucky is about 169.5 miles in diameter and represents the world’s supply of liquid freshwater. Out of the total water supply, 99 percent is groundwater, much of which is not accessible to humans. The sphere over Atlanta, Georgia is about 34.9 miles in diameter and represents freshwater in all the lakes and rivers on the planet.

3. On July 28, 2010, the United Nations General Assembly passed Resolution 64/292, which explicitly recognized the human right to water and sanitation and acknowledged that clean drinking water and sanitation are essential to the realization of all human rights. The Resolution calls upon States and international organizations to provide financial resources, help capacity-building and technology transfer to help countries, in particular developing countries, to provide safe, clean, accessible and affordable drinking water and sanitation for all.

4. According to the UN, 2.1 billion people lack access to safely managed drinking water services and 4.5 billion people lack safely managed sanitation services. Water scarcity affects four out of every 10 people on the planet and 340,000 children under five die every year from diarrheal diseases related to poor sanitation and unsafe drinking water.

5. In the United States, as many as 63 million people—nearly a fifth of the population—were exposed to potentially unsafe water more than once during the past decade, according to an investigation of 680,000 water quality and monitoring violations from the Environmental Protection Agency. And a study published last month in the Proceedings of the National Academy of Sciences found that health-based drinking water quality violations are so widespread that from 9–45 million people were possibly affected during each of the past 34 years.