Which of the following are the two main types of water storage?

The correct answer identifies the two main types of water storage as surface storage and subsurface storage. Surface storage refers to water that is stored on the Earth's surface in reservoirs, lakes, and ponds, where it can be easily accessed for various uses, such as agriculture, municipal supply, and recreation. This type of storage is crucial for managing seasonal variations in water availability and ensuring a steady supply during dry periods.

Subsurface storage, on the other hand, involves water held within underground aquifers and soils. This type of storage is vital for groundwater supplies, which can be tapped for irrigation, drinking water, and industrial uses. Subsurface storage often plays a significant role in maintaining water levels and replenishing surface water bodies through natural processes.

In contrast, other options such as river storage and ocean storage do not accurately represent recognized categories of water storage in the same way. Desalination and evaporation also do not fit into the typical classifications of how water is stored; instead, they relate to the processes of transforming water for use or loss rather than storage per se. Thus, surface and subsurface storage are the two main types of storage systems as they encompass the primary ways water is retained for human use and ecological balance.