Final answer:
The percentage of available freshwater that is unnecessarily wasted varies, but it is clear that a significant amount is being wasted globally.
Step-by-step explanation:
The percentage of available freshwater that is unnecessarily wasted in the world and the United States can vary depending on several factors. According to the information provided, water withdrawal as a percentage of total available water falls into different ranges: more than 40%, from 40% to 20%, from 20% to 10%, and less than 10%. Therefore, it is not possible to determine the exact percentage without more specific data. However, it is clear that a significant amount of freshwater is being wasted around the world.