can you proof read

When we turn on the top,we expect an abundant supply of clean, fresh water to flow out. Having one of the world's largest supplies of fresh water, these expectations may usually be met in Canada . However,in many other countries, water is a scarce commodity. Useless for drinking or agriculture needs unless the salt is removed the world contains much less fresh water (2.5 percent) than it does salt water (97.5 percent). The united nation say that in 25 years, two thirds of the world can be experiencing water shortages.

When we turn on the tap,we expect an abundant supply of clean, fresh water to flow out. Having one of the world's largest supplies of fresh water, these expectations may usually be met in Canada . However,in many other countries, water is a scarce commodity. Salt water is useless for drinking or agriculture unless the salt is removed. The world contains much less fresh water (2.5 percent) than it does salt water (97.5 percent). The United Nations says that in 25 years, two thirds of the world can be experiencing water shortages.

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Sure, I can help you proofread your text. Here is the revised version:

"When we turn on the tap, we expect an abundant supply of clean, fresh water to flow out. Canada is known for having one of the world's largest supplies of fresh water, so these expectations are generally met there. However, in many other countries, water is a scarce commodity and cannot be used for drinking or agriculture without removing the salt. The world's fresh water resources account for only 2.5 percent, while salt water makes up the remaining 97.5 percent. The United Nations predicts that in 25 years, two-thirds of the world's population will experience water shortages."

Please note that I made a few changes to improve the clarity and flow of the text.