Cisterns making a comeback

The Keys have always had cisterns.

The environmental movement has attracted new interest to the ancient technology, which uses storage tanks to store collected rainfall. They can be underground (such as converted septic tanks), at ground level, or on elevated stands that use gravity feed instead of a pump to deliver the water, even when the power is off. When their water is not pure enough for drinking, they can be used for irrigation purposes. Cisterns sanitary enough to store potable water can be used to offset the need for utility-supplied drinking water.

Another benefit of cisterns is that they can divert water from buildings, streets and parking lots that would otherwise become stormwater runoff — greasy, dirty water that ends up in the ocean or bay, damaging the living reef that surrounds the Keys.

Cisterns 101

Cisterns must be watertight, have smooth interior surfaces, enclosed lids and be large enough to provide adequate storage. They are usually made from materials such as reinforced concrete, galvanized steel or plastic

The rainwater is first collected in a catchment area. Galvanized steel and aluminum roofs are common, and gutters and downspouts carry the water to the cistern.

Gutter guards made of quarter-inch to half-inch mesh hardware cloth placed over the gutters keep out leaves and other large objects. Sand, gravel or charcoal filters are sometimes used to filter water before it enters the cistern but they require frequent maintenance to prevent contamination.

Roof washers are cheaper to construct and need less maintenance than filters. A roof washer traps the first flow from the roof and channels this dirty water away from the cistern. After the first flow, the water from the rest of the rainfall flows to the cistern.

A new cistern should be cleaned with a disinfecting solution such as chlorine bleach. An open cistern used for irrigation can attract mosquito larvae, so a pesticide may be required.

History of cisterns

Key West has a long history of cistern use, going back before the aqueduct was built or even before Flagler’s railroad carried freshwater down from the mainland in the early 1900s. Even the first Keys residents, the Calusa Indians, used natural freshwater wells. Today many old buildings still have cisterns, such as Old Town Manor Bed and Breakfast, which advertises a room with “a cozy private bath with a walk-in shower, built inside Key West’s tallest cistern.”

The Navy laid the first water-carrying aqueduct during World War II. Until then, Key Westers had but two sources of water — rain or train.

Later, the Conchs learned how to catch and conserve rainwater. Not long after the island’s first permanent settlers arrived in the 1820s, they discovered that the freshwater wells were being depleted, and brackish water was seeping in. So they learned how to build cisterns.

Cisterns even predated fallout shelters as a safe haven in times of peril. During the famous Indian Key massacre of 1838, nearly all who escaped did so by hiding in cisterns built under their homes Many survivors remained in water up to their necks for five or six hours while their houses burned above.

After the destruction of the railroad from the 1935 hurricane, the large quantities of fresh water transported by huge railroad tank cars also ceased. In 1941, the Navy built a pipeline with the Florida Keys Aqueduct Commission paying one third of the cost. Florida City was used as a well site. 128 miles of 18-inch pipe were laid from the Florida City site to Key West.

Although many cisterns were abandoned or destroyed after the Navy’s pipe came in, there are still hundreds on the island. Henry Flagler, builder of the railway that linked Key West to the mainland, put a million-gallon cistern beneath his Casa Marina Hotel back in 1922, and it’s still being used to water the grounds.


John Hammerstrom, an airline pilot, and Diane Marshall, a creative writing teacher at Florida International University, built their showcase “green” home in 2002. Marshall, who wanted to share what they learned, helped create the Keys Green Living and Energy Education Expo.

Following a long Florida Keys tradition, Hammerstrom and Marshall have a rain-fed cistern that uses a roof washer design to divert rainwater. The first rain off the roof, which holds the most dirt and debris, is allowed to drain away. Gradually, a ping-pong size ball lowers into the drain and clean water then is backed into the cistern. After a day, the drain stopper gradually rises again.

The cistern is divided in half, with the first compartment decanting water into the second. Hammerstrom uses filters to purify the water before it is brought into the house: a 1-micron filter for fine sediment, a carbon filter for chemical contaminants and a UV filter chamber for water sterilization.

A dual-source design lets them use city water or cistern water as necessary. Three valves control where the water comes from and goes to. Valve 1 delivers water to the kitchen island sink. Valve 2 brings water to the sinks, laundry and showers throughout the house. Valve 3 delivers water to toilets and outdoor hose bibs.

The water to the kitchen sink always comes from the cistern, and if it contains more than 600 gallons of water, the laundry, sinks and showers share the water. As the level drops, the hoses and toilets are switched to city water.

“There are no rules about how big a cistern can be,” Hammerstrom says. “The only requirement is that it meet the code for structures and permits. There are rainwater collection vessels of all description — from rain barrels made from recycled 55-gallon fruit juice drums to the newest and one of the largest [30,000 gallons] cistern in the Keys — at the Florida Keys Electric Cooperative building being constructed in Tavernier.”

But can you drink it?

Hammerstrom says yes. “Because most, if not all utility water is pumped from the ground, they have a disadvantage compared to rainwater harvesters because water — the universal solvent — picks up any contaminants that are present. When the water one uses is pumped from the ground, all of the chemical contaminants of our modern society are potentially present and can be pumped along with the ground water.

“Utilities spend lots of money to clean up the water, and the Florida Keys Aqueduct Authority is one of the best. The U.S. Environmental Protection Agency has a long list of contaminants that are allowed in small quantities, however. In the news lately is the fact that the EPA does not require testing for, nor do they have standards for a broad category of chemicals known as Personal Care Products and Pharmaceuticals.

“Rainwater, however, suffers from fewer contaminants. Rain is fundamentally distilled water. It evaporates from surface sources, becomes a cloud and then precipitates the condensed water back to earth. There are airborne contaminants, but in the Keys, and in South Florida in general, we have far fewer airborne contaminants than folks downwind of a coal-fired power plant, for example.

“Removing those potential airborne contaminants from rainwater is much less difficult than removing the much longer list of contaminants from ground water.

“As a result, we use the filtered rainwater for our primary drinking and cooking water source. It is very pure and tastes great.”

Septic-to-cistern conversions

Hookup to a central sewer system used to mean that your old septic tank had to be “abandoned” — that is, emptied and filled with sand to make sure it was safe and never used again.

But Fran Wagner of Key West’s Bay Point neighborhood felt that there was a better way, so he converted his old septic tank to a rainwater cistern. (See details on Page 10.) He went before the Monroe County Board of County Commissioners, who unanimously agreed to add their support. The Florida Department of Health also supported his plan.

The original health requirement gave only one option: remove or abandon the old tank. It had to be pumped out, cleaned with bleach, and filled with sand, all subject to their approval, within 90 days.

So Wagner became a pioneer in the battle to make cisterns a workable option. He applied to the health department for a variance. He says residents who have done their own conversions pay around $300 to $400 in costs, while having a contractor do it can cost $1,200 to $1,500.

Long-term savings offset those costs as “free” cistern water replaces piped-in aqueduct water, which will carry dual costs for both water and sewer service once the new sewer system is online. The initial septic-to-cistern conversion will cost more than merely abandoning the septic tank, but monthly savings should more than make up the difference over time.

The FKAA is working with the South Florida Water Management District to secure a grant to help fund construction of residential cisterns and septic-to-cistern conversions.

What’s the price tag?

According to Hammerstrom, “The cost of the storage portion of a new cistern is roughly a dollar a gallon. There are fixed costs associated with gutters, downspouts, pumps, plumbing, filters (if desired) and fixtures. The range of those costs can run from the simplest of non-potable systems that use existing gutters and downspout and is gravity fed through a hose bib at minimal cost, to a fully integrated system used within one’s home or business that included food-grade components and high-end purification.

“For the high-end cost, I’d estimate the cost of the components to be perhaps $2,000 fixed cost with an additional $250 per year to replace filters and other consumables (like the ultraviolet light in my system). The cost to install would vary widely with one of the variables being whether it is new construction or retrofitted.”

Converting septic to cistern can be less expensive. Wagner says his conversion of a 1,000-gallon septic tank cost only $740. “And that included $500 for the tank’s pump-out, which has to be done anyway,” he said. “So that’s a net $240. I did it all myself, so a plumber would cost more.”

“I estimate that we are getting about 3,000 gallons of water a year from our tank, so it will take awhile to break even. But our municipal water costs went up when the sewer system was hooked up. Also, when watering restrictions are in effect, we’ll still have water to irrigate with.”

Rain barrelsRainwater barrels are beginning to dot the Keys landscape, sometimes given out free at events like last year’s GLEE Expo. These mini-cisterns employ rainwater harvesting for limited irrigation purposes, such as garden watering.

If you didn’t get one of the free barrels, you can make one out of an inexpensive 50-gallon food-grade drum used to carry juices, olives, pickles, etc. Often you can find barrels for around $10 from drum and barrel suppliers. Be sure to get a heavy-grade plastic container that won’t let in light — clear or translucent barrels can speed the growth of algae which can clog pipes.

A rain barrel can also help reduce the amount of water that settles around the foundation of your home. You can hook it up to a soaker hose (with the pressure-reducing washer removed) to slow-irrigate your garden. Or you can use it to fill a watering can, keep your compost bin moist, or just rinse off your gardening tools.

A typical 1/2-inch rainfall will fill a 50- to 55-gallon barrel. Figure about a half gallon of water per square foot of roof area during a 1-inch rainfall. A 2,000-square-foot roof can collect about 1,000 gallons of water (accounting for about 20 percent loss from evaporation, runoff and splash).

Rainwater is better for your plants and helps conserve our supply of drinkable water. Check with your local GreenThumb certified nursery for their schedule of free tain barrel workshops for the public. The two-hour workshop will show you how to make your own 50-gallon rain barrel, how to set it up at your house, and other inventive uses. The main prerequisite is that you have a gutter system with a downspout.

To sign up, contact Cristina Lindley at the Monroe County Extension Office: 305-292-4501 or Lindley-Cristina@MonroeCounty-FL.Gov.