Water vs Waters

 Water is usually used as a noncount noun, but the form waters is sometimes used. Editor Kory Stamper helps explain the difference.

What's the difference between "the gray water of the Mississippi" and "the gray waters of the Mississippi"?

Both the noncount water and the plural waters are used to refer to a specific body of water, as in "the water(s) of Lake Michigan."  But there are subtle differences in their use. 

The noncount water is also used generally of any water, whether it is in small quantities ("a glass of water") or in large quantities ("We went swimming but the water was too cold."). 

The plural waters, on the other hand, is used especially of an area of seawater, and tends to appear in more formal contexts ("shipping lanes in international waters") and in literary contexts ("the azure skies and clear waters of the Pacific").

If you are not sure which one to use, choose water as it is the more versatile and less formal of the two.