Which type of clouds are typically composed almost entirely of water?

Low clouds are typically composed almost entirely of water. These clouds generally form at lower altitudes, typically below 6,500 feet, and are characterized by their thick, moisture-laden appearance. Clouds in this category, such as stratus and nimbostratus, consist mainly of water droplets, which is why they often bring precipitation.

In contrast, high clouds, which form at altitudes above 20,000 feet, can contain ice crystals due to lower temperatures, while middle clouds may consist of both water and ice, especially when temperatures are near freezing. Stratus clouds, while a type of low cloud, represent just one aspect of low clouds overall and do not encompass all low cloud types. Therefore, the classification of low clouds as primarily water-based makes them the most fitting choice in this context.