Final answer:
The least amount of water relative to the human population globally can be found in the Sahara Desert, while in North America, Death Valley is notably water-stressed. These areas have limited human settlements primarily around oases or sustain populations through extensive water conservation projects.
Step-by-step explanation:
The regions with the least amount of water available relative to the human population are typically arid and semi-arid areas with large deserts. For the global perspective, the Sahara Desert is notably one of the most water-stressed environments on Earth. It has extremely harsh conditions for both plant and animal life, with human settlements limited to areas surrounding oases, which comprise a very small fraction of its total land area.
In North America, the regions most affected by water scarcity include the American Southwest, with areas like California facing significant challenges. Urban areas in this region can sustain their populations largely due to extensive water conservation projects. Specifically, Death Valley in California is one of the driest places in North America.
Thus, the correct answers to the question are A) Sahara Desert; Death Valley, considering the conditions outlined.