Thomas, St. John and Water Island. The Virgin Islands rely on ocean water desalination to supply fresh water to residents and tourists. In addition all hotels collect rain water on their rooftops.

In 2026, St. Thomas in the U.S. Virgin Islands relies on a multi-faceted approach to fresh water, as the island lacks natural rivers or large freshwater lakes. The primary industrial source is desalination, managed by the Virgin Islands Water and Power Authority (WAPA). This process typically uses Reverse Osmosis (RO) to convert seawater into potable water, which is then pumped through a municipal pipe system to urban areas like Charlotte Amalie. However, because the municipal infrastructure doesn't reach every part of the steep, volcanic terrain, the most traditional and widespread method is rainwater harvesting. By local law, every house must have a cistern—a large underground storage tank—that collects runoff from the roof. For residents whose cisterns run dry during the Caribbean's "dry season" (January–May), water must be purchased from private "water haulers" who deliver thousands of gallons via specialized trucks. This system creates a culture of extreme water conservation among locals, as every gallon is literally "saved for a rainy day."