Which of the following is NOT considered a natural source of water?

Water tanks are not considered a natural source of water because they are man-made structures designed to store water. Unlike lakes, streams, and ponds, which are formed through natural processes such as glacial activity, rainfall, and runoff, water tanks are specifically constructed by humans to collect and hold water for various uses, including drinking water supply, irrigation, or fire protection. The other options represent ecosystems that naturally accumulate water in different forms, making them integral components of the natural hydrological cycle. In contrast, water tanks rely on external water sources and human intervention for their existence and functionality.