What you need to know about drinking water in St. Croix
Unlike many places stateside, St. Croix doesn’t have reservoirs and comprehensive municipal water and sewer systems. Water service from WAPA, a.k.a., the Water and Power Authority, is only available in and near the towns of Christiansted and Frederiksted. With well water also not usually a viable option, the rest of St. Croix relies on the sky for its potable water — namely, the capture and storage of rainwater using cisterns.
What is a cistern?
As far as building infrastructure goes, cisterns are actually a pretty simple system. Gutters along the roofline of a home capture rainwater, but instead of sending it down and out into the yard, pipes direct the collected water underneath the home into one or two large concrete receptacles, not unlike windowless cellars — these are the cisterns. A water pump draws the water up and through the pipes of the home for use.
How much does a cistern hold?
For new construction single-story homes, the roof-to-cistern ratio in the VI building code requires that the cistern must accommodate 10 gallons for every square foot of roof space. Unfortunately, you can’t use this equation in reverse for many existing houses, as it’s common for Caribbean homes to be expanded out rather than up when more interior square footage is desired. To know a cistern’s capacity, you’ll need to get the dimensions — length, width, and max depth — to calculate the cubic footage and convert that into gallons.
How can you tell how much cistern water you have?
Somewhere on the floor inside the home, you’ll find one or two cistern access lids, which are heavy 2-foot by 2-foot panels that lift out to allow human access for inspection, cleaning, or recoating (more on this in a moment). At the center of the hatch is a small removable metal plug. The most common way to measure how much water there is inside a cistern is to use a long piece of 1×1 lumber, marked with a permanent marker in 1-foot increments, as a giant dipstick that you insert through that center hole. Pull it straight back up and you’ll see a damp line that indicates the depth of the cistern water. If you know your cistern dimensions, you can use that depth to calculate the water in cubic footage and convert to gallons, as described above. During times of drought, you’ll want to check your cistern level regularly, as you definitely do not want to run dry and risk burning out your water pump.
Why two cisterns can be better than one
In homes that have two cisterns — or, commonly, one cistern with a bifurcating internal wall — the water can equalize by flowing between the two sides if one cistern becomes full and the other is not. The two-sided system also allows you use the water from one side while the other just fills, and if the first side becomes low, you can switch the draw over.
What if it rains a lot — or not enough?
During rainier times, cisterns eventually get full, and overflow pipes are in place to draw the water back out into the yard and away from the house. Typically the pipes that direct water down from the roof can be bypassed as well, so no additional water goes in. On the flip side, during a drought, you can order a tanker truckload of 3,000 gallons of water for around $400, usually for same-day delivery.
How do you take care of a cistern?
In terms of cistern maintenance, the VI Department of Health recommends regular cleaning of roofs, gutters, and the cistern itself. To ensure the safety of the water you’re drinking, a three-stage water filtration system plus a UV light is very effective at removing sediment and killing any bacteria — just be sure to replace filters and the light bulb as recommended by the manufacturer. Treating cisterns with chlorine bleach, in particular after heavy rainfall, is also recommended. You will also want to get the inside recoated to ensure water tightness as needed (typically every five or so years).
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