The total amount of water on our planet has, theoretically, stayed the same since earth's formation. It's possible that the glass of water you drank earlier contains particles that once ran down the Ganges River, passed through the digestive system of a dinosaur, or even cooled a nuclear reactor. Of course, before it quenched your thirst, this water evaporated and fell as rain millions of times. Water can be polluted or misused, but never created or destroyed. According to a UNESCO study, it is estimated that the Earth contains about 1386 million cubic kilometers of water. However, 97.5% of this amount is saline water and only 2.5% is fresh water. Of this fresh water, most (68.7%) takes the form of permanent ice and snow in Antarctica, the Arctic, and in mountainous regions. Another 29.9% exists as groundwater. Ultimately, only 0.26% of the total amount of fresh water on Earth is available in lakes, reservoirs, and watersheds, where it is easily accessible for the world's economic and vital needs. With the population steadily increasing, especially in urban areas, several countries have already had severe problems with providing the necessary amount of drinking water to their populations.