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Cisterns 101: Residential Water Supply in the USVI

One marked difference between home ownership stateside and in the U.S. Virgin Islands is residential water supply.  Island homes are required to be built with cisterns, which are large holding tanks that collect rain for running water.


Cisterns work by collecting rain water which falls on the roof of a home, and routing it down to a concrete holding tank lined in waterproof coating.  The rain supplies all running water for the home.  It is fine to use for showers, toilets, etc.  Properly treated cistern water is safe for cooking (see maintenance below).

Drinking Water

Opinions vary on whether or not cistern water is safe to drink (many locals and long-term stateside residents do).  But the best bet is to add a filtration system to one tap, which uses UV light or another treatment to clean the water (a typical pitcher-type system using charcoal filters is insufficient).  Some refrigerators have filtration systems built-in which are able to convert the cistern supply for drinking water and ice.  Many St. Croix residents opt to purchase drinking water by the gallon, or refill larger containers at machines found at every grocery store and some gas stations (as of November 2014, the cost is 65 cents per gallon).


It is important to add bleach to your cistern regularly to eliminate microbial growth.  The rule of thumb is 1 tablespoon of bleach per 100 gallons of water if the cistern is clean.  So you will need to know the exact cubic measurements of your cistern, use a measuring stick to find the water line and calculate accordingly (you can find more detailed instructions on eHow).

An annual inspection of your cistern by a professional is also a good idea.  They can advise whether it’s time for a cleaning or re-coating of the interior of the cistern, or a re-coating of the roof to optimize rain collection.  Contact a company like ClearWater Roof and Cistern.

City Water

For homes located right in Christiansted or Frederiksted or close by, city water supply is also available for which you pay the Water and Power Authority (WAPA) by the gallon.  Rates vary monthly, but as of March 2014 the residential price was $18.56 for the first 1000 gallons (approximately 2 cents per gallon).

Water Delivery 

If your cistern should run dry (aka “flat”) water delivery services are available by truck from companies like MARCO.  Pricing varies based on delivery location, but as of November 2014, 3300 gallons of well water costs approximately $170 (5 cents per gallon) or the same amount of desalinized water costs $260 (7 cents per gallon).

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