IS 7 hereon RESOURCES OF THE RESEARCH VIRGIN ISLANDS CENTER . . CAPSULE REPORT NO. 1 Caribbean Research Institute AUGUST 1985 ESTIMATED WATER USE IN ST. THOMAS, U.S. VIRGIN ISLANDS July 1983 - June 1984 B Heriberto Torres-Sierra and Rafael Dacosta INTRODUCTION The population of St. Thomas, U.S.V.L. has risen from 16,000 in 1960 to more than 47,000 in 1984, During this period there has also been an increase in tourism. The demand for water has increased in response to this rise in population and tourism. The need to determine the amount of water used to meet public, commercial and domestic needs, among other uses, is essential where, as in St. Thomas, the available supply is inadequate. WATER SOURCES AND USES Sources The principal sources of water on St. Thomas are sea water, d from rooftop and stored in cisterns, and groundwater. 93.72 million gallons of sea water are used daily on the island. Rainfall provides 0.65 million gallons a day and groundwater accounts for 0.35 million gallons per day, Uses The generation of electric power, the Public- -water supply, public sewage and self-supp ial and com- mercial blish are the principal users of water. Ther- moelectric power generation is the largest single use category in St. Thomas. Over 67 million gallons of sea water are used daily by the Virgin Islands Water and Power Authority (WAPA) to cool its condensers used in electric power generation. | £ | bolees GROUND WATER, | 0.05 MOO | RAINFALL 65 MGO PF - Thermoelectric Power WS - Public. Supply 00 ~ Domentic SALINE WATER 93.72 MGO CO - Commeccia! FIGURE 1: Estimated use by source and Category in St Thomas during Suiy1003 10 903 10 June 1904." PUBLIC WATER SUPPLY Desalinated Water Waste heat from WAPA’s electric generators is used by the sea water desalination plant. Desalii d water is stored in tanks and distributed to the island’s main urban center, Char- lotte Amalie, by the Virgin Islands Public Works Department (VIPWD). Production of desalinated water ged 2.4 million gallons per day during the study period. Of this 2.4 million gallons, only 0.9 million gallons were accounted for (revenue from sales) by the VIPWD. The other 1.5 million gallons per day were unaccounted for. This is due mostly to losses from leakages in the distribution system installed in 1949. Other losses are due to unauthorized connections, faulty meters and uncontrolled public faucets, The cost of potable water to WAPA from the desalination plant is about $9.00 per 1000 gallons. Sea Water Distribution System Water pumped into the sea water distribution system average about | million gallons a day. Approximately 0.35 million gallons of this sea water are accounted for daily at the public sewage treatment plant. The remainder is used to flush storm drains, fight fires or is lost through leaks in the sea water dis- tribution system. DOMESTIC SELF-SUPPLIED Rainfall Nearly two thirds of the population of St. Thomas is not ser- ved by the potable waterdistribution system and these users are classified as domestic self-supplied, Estimated water use in this category was about 0.75 million gallons a day. Of this amount, 0.60 million gallons (80%) was supplied from rainfall. Virgin Islands’ law requires all dwellings, apartments and hotels to have a mini cistern storag 'y of 10 gallons for each square foot of roof area for one story buildings and fif- teen gallons for each square foot of roof area for buildings of two or more stories. Churches and warehouses are not required to conform to this standard. Groundwater G d for domestic self- lied use is around 0.15 million gallons daily.G di for d ic use is availabl in nearly all parts of the island. However, there are only a few areas where yields to wells are large enough to warrant the development of public supplies. Furthermore, the potential yield and water quality is limited by excessive depth to the water, sea RAINFALL 0.65 GROUND OCEAN 90.92 STREAMS 0.13 Public Sewage Plant Domestic 8) 0 Supplied LAND 0.87 WATER 0.35 —— water Lost FIGURE 2: Water sources, Thomas, in million gallons per day. water i ion, waste water from sea water mains. COMMERCIAL SELF-SUPPLIED Condominiums and hotels use about 2 million gallons of salt water daily. This water is used primarily for cooling, flushing toilets and for swimming pools. Small desalination plants pro- duce about 0.1 million gallons of fresh water per day. Around 0. 2 -— gallons ty water used daily by hotels and ial water haulers sup- ply about 0.07 ‘mullion gallons i desalinated water from the VIPWD standpipes to users in the hotels and condominiums. PUBLIC WASTE-WATER TREATMENT There are seven public waste-water treatment facilities on St. Thomas. One serving Charlotte Amalie and the other six serv- ing mostly public housing projects. These public waste-water treatment plants discharge nearly 0.7 million gallons daily into streams and the ocean. * To St. John and Culebra uses, disposition and amount for each use category in St. Condensed by Yahaya Bello from: “Estimated Water Use in St. Thomas U.S. Virgin Islands, June 1983-June 1984” by Heriberto Torres-Sierra and Rafael Dacosta, Technical Re- port No. 21, Water Resources Research Center, Caribbean Research Institute, St. Thomas, September 1984. For further information on this report contact: Water Resources Research Center College of the Virgin Islands St. Thomas, Virgin Islands 00802 (809) 774-9200 The research on which this report is based was financed in part by the United States Department of the Interior, Geological Survey, through the Water Resources Research Institute. 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