The correct answer is: A. It reduces the water resources that are available for other uses.
Depletion of water resources due to irrigation can limit the availability of water for other purposes, such as drinking, sanitation, industrial use, and supporting ecosystems. While increased salinity and environmental changes can occur (as mentioned in options B and C), the primary effect of depletion is the reduction of available water resources for various needs. Option D is incorrect as depletion does not help countries with growing populations; rather, it can exacerbate water scarcity issues.