Which of the two Polar Ice Caps is Mars's primary source of water?

The North Polar Ice Cap is considered Mars's primary source of water because it contains a significant amount of water ice. This ice cap is composed primarily of water, unlike the South Polar Ice Cap, which is largely made up of carbon dioxide frost with a smaller proportion of water ice. The North Polar Ice Cap's extensive ice deposits are critical for understanding Martian climate and potential for past or present life, as they are thought to have a more stable and substantial volume of water relative to the South Polar region.

Additionally, research indicates that the North Polar Ice Cap undergoes seasonal changes, which suggest the presence of water in various forms, such as sublimation and deposition cycles. This cycle plays a crucial role in studying Mars's water history and its geological processes. Thus, the North Polar Ice Cap's substantial ice reserves make it a focal point in discussions about water on Mars.