What size cistern?

The cistern size that is right for each property depends on several factors, such as the number of bedrooms/people who will be using the water and the location on the island. Location is a big factor since some areas get more rain regularly and a smaller cistern is OK, while areas with less frequent rainfall require larger cisterns to hoard every bit of the water that can be collected during the rainier seasons (typically May & October are very wet all over the STX). Most cisterns are constructed with at least two chambers. You draw from one at a time and can switch between them. Most have a feature that allows water to spill from one into the other if the one you aren't using is full. If you don't have the spillover feature, excess rainfall dumps out through an overflow pipe and is lost. In this type of system, you need to be more careful to check the levels frequently and draw from the fullest cistern to allow new rainfall to have as many places to collect as possible. If all cisterns are full, excess is still released through the overflow pipe.

Most 2-BDR properties have at least a 15K gallon capacity. Most 3-BDR properties have 20K gallon or larger. Lots of properties that have two or more units will have 30K to 50K of cistern capacity. Sometimes the units share all the cisterns and other times they each draw from a specific chamber but may still benefit from the spill over feature if other cisterns are full.

If you have a smaller than usual cistern, you need to be much more conscious of your water consumption rate and turn off faucets, etc. when not actually using them, take shorter showers, and that sort of thing. Rates for trucking in water are usually about $150 for a 5000 gallon truck load that will often last long enough to get you to the next rainy week. Nobody wants to pay for extra water, but if it's only a 1-2 time a year need towards the end of the dry spells it doesn't totally blow the budget. If you had to truck in water every month, it would add up fast. I've seen condo occupants with metered water service rack up water bills of over $200 per month, though. The first couple of bills make their eyes open wide and they have to change their water use habits.

Most properties you will look at to purchase will have adequate cisterns. If the size sounds small, talk to the people occupying the property and they may honestly tell you how often they have to buy water. If you try to move more people into a property than it was designed for, the cistern may not be large enough to cope with the unexpectedly high demand.

Remember west usually get more rainfall throughout the year so a smaller cistern on that side is not as big a deal.

Thank you so much, Alexandra & Betty! Very helpful 🙂

We are paying $300/5000 gallon truckload of water on St. Thomas.

I have been asking that same question as well. Our palce will be on the North Shore which gets less the the West end, but more than the East end. I've been told to figure the price on building at about $1 per gal. Do you spend an extra $30K or buy water once or twice a year at a couple of hundred bucks a load?
I am leaning toward a smaller one around 35k gal or smaller. there is a code on the min. size.

We live on the north shore of STX and our house has two cisterns (about 25,000 gallons total capacity). I have purchased water the last two years in April, not because we were out of water but for peace of mind because we down to a couple of feet in each cistern. The price for 3300 gallons of well water from Marco was $95 last year and $105 this year. Distilled water costs a little bit more ($285 for 5500 gallons from Marco) but we don't drink the cistern water and my toilets can't tell the difference. Also, it appears that my purchase of water is a very effective rain dance as both years we have had significant rainfall within days of my water purchase. So, assuming that you have to buy water once or twice a year, it might take a hundred years or so before you will have spent on water purchases that $30,000 you are thinking about spending up front for an extra cistern.

Thanks for the insight.

35K gallons is actually a pretty large size cistern for a small to mid-size house in the north shore area, which does get a lot of rainfall throughout most of the year. The one dry spell long enough to deplete cisterns down low is typically from January through March and maybe into April. Even if you used 5K gallons per month, most 20K to 25K cisterns don't run dry.

I live on the southwest shore and my house has two 25K gallon cisterns, but only because it was originally planned to be a 2-unit house. I have never depleted even one chamber of the cistern completely during the dry season.

I've been hearing that the cost of building cisterns is running closer to $2 per gallon lately since concrete prices have gone up so much the past two years.

I think we had a total of 25 or 30K gallons in 2 cisterns in la Grande Princess on StX and we only ever had to buy water when we filled the pool after cleaning etc. That was 5 or 6 years straight.

I hear people in stx refer to the North Shore getting lots of rain. I understand the East End is quite dry and West End is quite wet. So to help with my coordinates...what are the east and west boundaries that define the 'North Side'?

The "north shore" area is typically any part of the northwest shoreline along HWY 80. From west to east you have Annaly Bay, Davis Bay, North Star, Cane Bay, La Vallee, Rust Op Twist, Clairmont, Concordia, Salt River, Morningstar.

so that means Judiths Fancy is not too wet and not too dry?...somewhere in the middle?

yes

With weather patterns changing we have been getting more rain on the east end. Last spring we were grreener on the east end the many center island locations. We got 4" of rain this week while they got less than 2" at the airport.

My point being I'm not sure I would rely on history to predict what future rainfall patterns will be.

Jim

I live by the airport and we've had far more than 2" of rain this week.

The rain pattern on the island is determined by the topography of the island and the prevailing wind pattern. With the wind coming from the east the vast majority of the time, it sweeps across the eastern section of the island, evaporating moisture and carrying it along as it heads west. As the hills rise along the way, the moisture rises and condenses and eventually produces some rainfall by the time it reaches the hills of the northwest portion of the island. This is in addition to rainfall from the larger storm systems that arrive at the island already prepared to dump water everywhere, but again the hills of the west end create an uprise that encourages condensation and an increase in quantity of rain.

Alexandra,
Not only should you be mayor, now I think you should be official Jim Cantori of the USVI's. Thanks for the education.