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Tank Town

For over 100 years, they’ve supplied water for your needs – but what do you really know about them? A primer.

Renee Serlin, the president of her Manhattan co-op, produced and directed documentary films in England. She wrote “Prep Work” in the May Habitat.

If you live in a building taller than six stories, you probably have a New York City icon on top of your rooftop: a water tank.

Many people wax lyrical over these structures. But, if you haven’t walked through the city streets looking up at them, then you may also have missed these huge wooden barrels, raised high on stilts, which seem to be wearing conical hats. Rumor has it that the most frequently asked question by tourists is, “What are those things on all the roofs?”

Buildings that have fewer than six stories don’t have such reservoirs. They don’t need them. The city’s water flows into buildings with just enough pressure to raise the water to the first six stories. With the advent of elevators and taller buildings, there was a need to find some way of supplying the higher floors with water at sufficient pressure to flow out of the faucets when they were opened.

Elevators were commercially available by the 1860s and, by the 1890s, barrel-maker Abraham Isseks had the idea that if barrels could hold wine and beer, they could also be the ideal way to store gallons of water on a building’s roof. Water pressure wouldn’t get the water up there, but a basement pump could lift the water and, once in the tank, gravity would do the rest. It was a simple solution with a dual impact. Not only did it supply water for household use and drinking, it also provided a reservoir of water for firefighting.

This secondary use became so important that around the turn of the 19th century, tenements higher than six floors were legally required to have a water tank visibly standing on the roof. More than 100 years later, buildings over 75 feet tall are using much the same technology and almost identical wooden water tanks. And, four generations later, Abraham Isseks’ great-grandchildren – brothers Scott and David and sister Beth Hochhauser – are still in the business.

Tanks a Lot

Water tanks are typically constructed of three-inch-thick planks of wood, usually cedar, which are bound together with circular iron hoops. Hidden from view, but resting on the walls is a flat wooden cover and, above that, a conical roof made from pine or plywood. The whole structure is mounted on steel supports that lift the tank some 15 to 20 feet above the roof surface. David Hochhauser says the tanks last a minimum of 20 to 25 years and, with proper maintenance, could have a useful life of 40 years.

The water tank business is unusual. The three New York City tank manufacturing and maintenance companies are all family firms, at least 100 years old each. Rosenwach Tanks was founded in 1896 by the great-grandfather of Andy Rosenwach, the current owner. Richard and Steven Silver (father and son) are owners of the American Pipe and Tank Lining Company, a firm that was founded in 1904 by Richard’s father.

Rosenwach estimates that there are over 10,000 wooden tanks throughout the city’s five boroughs. They may be constructed according to tradition, but the Department of Buildings has very specific requirements for every detail of the piping and operation of the tanks, and the Department of Health and Mental Hygiene regulates, in great detail, the procedure for safeguarding the potability of the domestic water in the tank.

The greater proportion of residential apartment buildings draws its drinking water from these tanks, and the city requires that they receive annual cleaning and disinfection. Andy Rosenwach suggests that the quality of the water in the tanks is probably higher than the quality coming directly from the street mains. Water flowing through the latter picks up all manner of sediment and algae from the pipes and it’s all pumped up into the roof tanks.

But, at that point, an interesting phenomenon occurs. Because the bottom part of the tank contains the water that has to be reserved, by code, for firefighting, only the water from the top half is drawn off for domestic use – drinking, cooking, showering, flushing toilets – and the tank acts as a kind of settling basin to allow sediment to filter down to the bottom.

By city fire code, there are hose connections on every floor mounted on the wall of the building’s stairwell. In an emergency, firefighters can immediately tap into the roof reservoir from any floor. An average 10-foot-high-by-12-foot-wide diameter tank holds 10,000 gallons of water; code requires that 3,500 gallons are reserved for standpipe use. If a building has more than two stairwells equipped with standpipes, then 5,000 gallons has to be reserved.

Care and Feeding

One of the most important recommendations for any building with a roof tank is to have building staff go up to the roof every week to check for any sign of overflows, or any wear and tear on the pipe insulation or other parts of the structure. Primarily, they need to check regularly to see whether the tank has any leaks.

A more thorough inspection, of course, is provided as part of the annual maintenance contract that all three companies offer. If any leaks have been reported, the hoops will be tightened with a wrench. The hoops are not easy to reach, says Hochhauser, who notes: “We use a boson’s chair, like on a ship.” It’s slung from the center post that rises out of the conical roof. The contracts also guarantee a year’s worth of free callbacks if any leaks develop during the year.

Before a crew arrives to clean the tank, building personnel – usually the superintendent – are responsible for completely emptying out the water. Any super who knows what he’s doing turns off the pump hours earlier so that the domestic water is drawn off by the residents instead of being dumped. Then, only the remaining standpipe water has to be drained out.

The drainpipe opens onto the roof and the water runs off into a drain in the roof. When the tank is completely empty, the cleaning crew – usually two men – put on clean rubber boots, climb the metal stepladder running up the side of the tank, open a hatch or trap door in the conical roof, and climb down into the tank.

The cleaning is done the old-fashioned way, with squeegee mops, scrubbing brushes, brooms, and buckets. A bunghole at the lowest point in the tank floor is opened to allow all the muck and sediment to be swept out. Department of Health regulations specify exactly how the tank has to be disinfected (by using a chlorine solution). After the tank has been cleaned, most buildings opt to have a bacteriological test. For about $100 or $125, you get confirmation that the water is potable. (But this isn’t a code requirement.)

Stewart O’Brien, executive director of the Plumbers Foundation of the City of New York, is concerned that, at present, there is no enforcement mechanism to ensure that buildings comply with the requirement for an annual cleaning. “We tried to get a bill passed some ten years ago that said, when you clean the tank, you have to send a report to the city so that they know it’s been done.” However, it was strenuously opposed by the real estate lobby and didn’t pass. “So there is a requirement that the tanks be cleaned once a year, but nobody really has a good idea whether that’s being done or not.”

Steven Silver is more concerned with a code item that can, and, he believes, will be enforced: the requirement to deal with backflow prevention. Backflow became an issue when the state department of health introduced detailed regulations for potable water supplies in 1981. The city water board was made responsible for protecting the public water supply from pollution, and they produced something called “A Risk Assessment Chart.” It identifies situations where the devices are needed.

The obvious case is where there is a dry-cleaning store or a medical office. Less obvious is the inclusion of any building that has a combined tank (i.e., a store of domestic and fire standpipe water). Because the fire protection water is basically stagnant, the city has determined that, theoretically, it could be a hazard and the owners have to install a backflow valve on the water service into the building. The valve allows water to flow in to the building, but prevents any building water from backing up into the city water main. Silver believes that many buildings have neglected this requirement.

Inside the Tank

Tank operation is basically very simple and tanks are largely maintenance-free on a daily basis. The easiest way to see the inside of a tank is at the Learning Center, operated by Cooper Square Realty. A large model of a tank has been set up in the center of the room and allows you to see clearly how the system works.

Water is pumped up from the basement and enters at the top of the tank. City code requires that an air gap of at least four inches be maintained between the end of the inlet pipe and the water at its highest level. This prevents any tank water from being sucked back down into the feed pipe. Once the tank is full, a float in the water (acting much like the float in a toilet tank) triggers a switch that sends an automatic signal down to the basement pump to shut it down. As a fail-safe measure, in case the pump does not respond, there is an overflow pipe near the top of the tank and, in many tanks, another switch sets off an alarm to warn that the tank is overflowing
About a third of the way down, a pipe allows water to flow out to the apartments. None of the water below that outlet pipe is drawn out for domestic use (that’s the firefighting reserve). When the water reaches a point just above the outflow pipe, a float triggers the pump to start operating again. In between, the pump doesn’t operate and water is not drawn into the building until the roof reservoir needs refilling.

The switch boxes connected to the floats are mounted on top of the flat roof under the protection of the conical roof. Because of the continually damp atmosphere, however, it’s possible for the mechanisms to corrode. The biggest concern is that the basic switches use mercury. That substance is highly toxic and, although it’s unlikely, it is possible that the container could break and allow mercury to seep through the planks of the flat roof into the water reservoir below.
Alternate control mechanisms are available. One device uses high-voltage wires suspended in the water. As the liquid reaches sensors suspended at various levels, a circuit is completed and the pump mechanism or alarm is triggered. This is an improvement, but it still has a number of moving parts and requires a high-voltage connection. Rosenwach is passionate about innovating and, working with Joe Gentile at Gatesoft Technology, he has developed a new kind of low-voltage, floatless switch with no moving parts at all. Introduced last December, and still awaiting patent protection, the Abacus Floatless Control relies on the pressure of the water to detect levels.

Water Water Everywhere

In general, if a building has a roof tank, the distribution system will reach every floor. When there’s a power blackout, the advantage of having a tank is that you have an opportunity to store some of the water still available. But, once used up, that’s the end of the water supply: without electricity, the basement pump is dead, and along with everyone else, you’ll be running to the store to purchase water as well as batteries and candles.

However, some buildings discovered that, even though they had a tank that had used up all its reserves, they still had water coming out of their faucets. When the tanks were first introduced, many buildings were plumbed with a dual supply. The lower floors were connected to the city mains’ supply of water; only the upper floors were serviced from the tank. Post-World War II, the practice stopped and every floor was connected to the roof supply.

Almost all the tanks in New York City were made and installed by either Isseks or Rosenwach. Rosenwach is the only company with a plant located in the city; Isseks uses a facility in Philadelphia. Both companies also make and install steel tanks, but, generally, those are set up inside a building. For use on top of a roof, wood is ideal.

“It’s a natural insulator,” says Rosenwach. “Three inches of wood [are] equivalent to 24 inches of concrete and, in the hot summers, the water will stay cool, and it gives added thermal warmth to the water in the winter.”

When the tank is constructed, it usually leaks for the first day or so until the wood has absorbed water and expanded. But as long as the tank has water in it, it will stay watertight for years. Hochhauser advises that the wood has to be allowed to “breathe” –i.e.. to expand and contract with the weather, so there is never any paint or other material covering the wooden sides of the tank.

But the conical roof is not in contact with the tank water and it bears the brunt of any bad weather. This is the only part of the structure that has to be protected – typically, with a rubberoid coating. The coating lasts about five to ten years but bits of it can come loose and pull away, especially if there have been hurricane level winds or if the roof is battered by high winds coming off the river.

For the last three years, Rosenwach has been using an alternate coating called Dynagrip to provide extra resiliency to the conical roofs. The new substance is the same material that has been in use for some while on regular roofs so, in spite of the limited application to tank roofs, Rosenwach expects it to last for the lifetime of the tank. Those with the new coating can easily be spotted on the skyline because the cover is a bright tan color while the rubberoid coatings are black. If the underlying framework is in good condition and the plywood or pine strips are still sound, the new surface could be applied for about $1,800. If the wood and the frame have to be replaced, the cost could be closer to $4,000.

Tanks for the Memories?

The counter-intuitive situation with roof tanks is that people expect the water pressure to be highest just under the tank, on the top floors. But this is precisely where, if anywhere, there will be a problem with too little pressure. Immediately below the tank the pressure is lowest and only increases as the water drops further down the building. Code specifies that the tank has to be raised above the roof so that it’s at least 25 feet above the highest fire standpipe.

“People think that’s where the tank has to be,” says Richard Toder, a sanitary engineer who has designed water distribution systems for buildings throughout the city. But if you did it that way, you wouldn’t have adequate pressure to serve the fixtures. “The code says that the pressure supplied can be as low as 8 PSI (pounds per square inch).” When the code was originally written, showers had two handles instead of the mixing valve that’s now a requirement to prevent scalding. The new fixtures require about 30 pounds of pressure to operate. “So the height of a tank depends more on the fixtures you expect to supply at the top of the building, than on the calculations provided by the code.

As you get lower down in the building, you find the opposite problem: too much pressure for the pipes and fixtures. “The maximum pressure that you can have in the system is 85 pounds,” Toder says. So, depending on the height of the tank and how many floors there are in the building, you might need to install pressure-reducing valves in the lower section. Otherwise, you could find a high-pressure jet stream shooting out of your kitchen faucet.

For the future, the question is whether New York City is going to remain a tank town. In other cities, roof tanks have been almost totally abandoned in favor of pumping systems that push water up a building instead of allowing it to fall down. Chicago’s roof tanks were part of the frenzied response to the city’s devastation in the great fire of 1871. Today, there are only some 130 still in use, and last year the city sponsored a competition to find new uses for the relics still standing.

The energy required for most of those pumping systems greatly exceeds the amount needed for a set-up using tanks. But Toder confirms that in some new developments under 20 stories, developers are opting to install pumping systems. It’s in taller buildings that tanks are still holding their own. Isseks recently installed four 20,000 gallon tanks on the Time Warner Center in Columbus Circle. Rosenwach has installed them on buildings in Times Square. So, singing “Tanks for the memories” may be a bit premature.

Clean-Up Time

Cleaning your water tank? The majority of buildings that do opt for a comprehensive annual maintenance contract with a company that can take care of any problems with the tank and, most importantly, provide an annual inspection.

The inspection will make sure the insulation round the external pipes is in good shape; that tank covers are tight and will keep out airborne dirt and pigeons; and that the wood is not rotting. Repairing insulation or replacing wood or covering material will incur additional charges. But any hoop-tightening that’s indicated during the inspection will be taken care of as part of the contract. Most companies will also include a year-long warranty against leaks, as long as the wood is in good condition.

The cost of a contract can vary considerably depending on the size and condition of the tank and on whether the work is carried out during normal working hours or in overtime. Most residential buildings will want their tank cleaned during the day when a large proportion of the residents may be away at work. Prices can run anywhere from $500 or $600 up to $900 – and more if overtime is involved. Cleaning, without the annual contract, may be 10 percent less.
An additional benefit of an annual maintenance contract is that the water tank company will alert management when the annual cleaning is due.

Over the last ten years, many buildings are opting to add a water quality test to the annual cleaning operation. For an added $100-$125, an independent laboratory will check the quality of the water in the newly cleaned tank. This is not required by the city. Michael Borello of Environmental Building Solutions, one of the many laboratories that specialize in providing water quality testing, explained that they do a “presence/absence” test for coliform and for E-coli bacteria. The Federal Safe Water Drinking Act requires zero percent of these organisms to be present in drinking water, so any positive indication is enough to make the water fail the test.

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