Only about 1% is available for human use
Explanation
The Earth's hydrosphere consists primarily of saline water in oceans, with fresh water constituting a very small fraction. The distribution of this fresh water is heavily skewed towards inaccessible reserves such as ice caps and deep aquifers.
Option Analysis:
- It is evenly distributed globally is Incorrect: Fresh water is not evenly distributed globally. Its availability varies drastically depending on climatic zones, geography, and precipitation patterns (e.g., the abundance of water in tropical rainforests versus scarcity in arid deserts).
- 70% constitutes groundwater is Incorrect: Groundwater constitutes approximately 30.1% of the total fresh water. The majority of fresh water (about 68.7%) is locked up in ice caps and glaciers.
- Only about 1% is available for human use is Correct: While fresh water makes up roughly 2.5% to 3% of all water on Earth, the vast majority is frozen or underground. Consequently, only about 1% (specifically, readily accessible surface water like rivers and lakes) is easily available for human consumption and ecosystem support.
- It constitutes 50% of the total water volume is Incorrect: Fresh water constitutes only about 2.5% to 3% of the total water volume on Earth. The remaining ~97% is saline water found in oceans and seas.
Key Takeaway:
Although Earth is known as the "Blue Planet," fresh water accounts for less than 3% of the total water, and of that fraction, less than 1% is readily accessible for direct human use.