Water Island is the fourth and most recent main island in the U.S. Virgin Islands, a United States territory located in the Caribbean Sea. The island lies to the south of St. Thomas in the Charlotte Amalie harbor. The Water Island Ferry Service runs regularly from Crown Bay, St. Thomas to Phillips Landing on Water Island; the ferry ride takes about ten minutes.

At a little less than 500 acres in size, Water Island is the smallest of the main U.S. Virgin Islands. Water Island is a residential island, with a population of 161 (2000 census) and no significant commercial establishments. There are two restaurants located at Honeymoon Beach. It's the smallest of the US Virgin Islands. Water Island is referred to as a residential island, meaning it doesn't have hotels, taxis, public transportation or stores, except for the Virgin Islands Campground. Being a ten minute ferry ride to St. Thomas locals and visitors depend on that island for things such as provisions, education, flights, and mail service.

The earliest known settlers were the Taino Indians dating back to the 15th century. When the European settlers landed on the island they named it because it has lots of fresh water, which was lacking on many of the nearby islands. The Danish laid claim to the island in the late 1700s, and in the 18th and 19th century, freed slaves took ownership. The United States bought the island in 1944 to protect the submarine base on St. Thomas during World War II and in 1996 the US government transferred ownership to the territorial government making it a place for people to reside and now a place for visitors to enjoy.

The main attractions are beaches, including Honeymoon Beach, Limestone Bay, the plantation ruins, and Fort Segarra, an underground fort partially constructed by the U.S. during World War II.