Which of the following is more closely related to water quality rather than water quantity?

The focus on water quality rather than water quantity is best exemplified by sewage treatment facilities. These facilities are specifically designed to treat wastewater to remove contaminants before it is released back into the environment or reused. The primary goal of sewage treatment is to enhance the quality of water, ensuring that it meets health and safety standards for environmental discharge and potential human consumption.

In contrast, the other options primarily address aspects of water quantity. The depletion of aquifers pertains to the reduction of groundwater reserves and their ability to supply water for various uses. The construction of dams is generally aimed at regulating water flow, creating reservoirs for storage, and ensuring a steady supply of water, focusing on managing water levels and distribution rather than enhancing the quality. Crop irrigation relates to the efficient use and management of water resources for agricultural productivity, again focusing on quantity to ensure that crops receive sufficient water for growth.