How many percent of salt water can people drink?

Humans cannot drink salt water due to its high salinity, which leads to dehydration rather than hydration. While seawater is about 3.5% salt, the human kidneys can only excrete salt at concentrations less than this, making it harmful to consume. Drinking salt water can lead to increased thirst and can ultimately result in health complications. Therefore, the percentage of salt water that is safe for human consumption is effectively 0%.