Greenwater is a census-designated place (CDP) in the northwest United States in Pierce County, Washington. Southeast of Seattle, the population was 67 at the 2010 census, down from 91 in 2000. At the 2020 census, the population was 95.

Pierce County is a county in the U.S. state of Washington. As of the 2020 census, the population was 921,130, up from 795,225 in 2010, making it the second-most populous county in Washington, behind King County, and the 59th-most populous in the United States. The county seat and largest city is Tacoma. Formed out of Thurston County on December 22, 1852, by the legislature of Oregon Territory, it was named for U.S. President Franklin Pierce. Pierce County is in the Seattle metropolitan area.