MORE INFORMATION — QUESTION 1: Try carrying three gallons of bottled water in each hand up several flights of stairs and you begin to grasp the challenges of delivering water to millions living in high-rise New York.

Measures beyond simple plumbing are needed to deliver consistent pressure and supply during Super Bowl commercial breaks in apartment towers with hundreds of tenants. (An average flush uses the six gallons you hauled up the steps.)

And providing water to multistory structures is not a task for wimpy water pumps and plumbing. The higher you force water up a pipe, the longer the column of water becomes and the heavier it gets. Delivering water up a one-inch-diameter pipe to the top of the Empire State Building is equal to lugging a fully-grown male gorilla up 84 flights of stairs.

In most neighborhoods, pressure in the city's water mains will service taps up to and including the sixth floor. Much of New York's water system was designed long before anyone imagined a need for heavy lifting much beyond that height, let alone up pipes running as high as a quarter mile above street level.

How to hoist water skywards and maintain consistent pressure isn't just a concern of plumbing contractors. Firefighters also are required to defy gravity to quench upper-story infernos. And their job requires delivering vast quantities of water on very short notice.

The solution to all these challenges calls for one or more pumps, usually located in the basement, to boost water to the roof where it can drain into the structure's fire and household systems using the reliable force of gravity. To ensure an adequate supply at all times, a pedestal is built higher than the building itself, on top of which is placed a barrel-like reservoir large enough to hold several thousands gallons of water.

Hence, the hard to miss and very difficult to disguise New York City water tank.

Constructed of rot-resistant cedar or redwood, each tank is built using techniques practiced by barrel makers for centuries. Just as stones in a Roman arch are narrower on the inside of the arch to enhance the archway's stability and strength, so the staves of a water tank are slightly undercut towards the side facing in. When placed upright in a circle, the staves form a cylinder of surprising integrity.

Neither nails or glue are used to hold these boards in place. Instead, the circumference of this cylinder is wrapped with metal hoops tightened with bolts. Because the weight of water pushing outwards is greatest at the bottom of the barrel, the tank builders increase the number of hoops as they work downwards. When filled, the force of the water pushing outward, and the swelling of the wet wood against the hoops, soon creates a reasonably tight seal.

The untreated wood soon takes on a patina that makes almost all water tanks look decrepit. A tank may be old, some as many as 30 years, but most are not derelict. Periodic draining and cleaning of the tank's interior is required to remove, among other substances, tank sludge composed of impurities missed by the city's water treatment.

Here's how a typical system works. A float resembling a toilet-tank shutoff sends a signal when water in the tank recedes, starting the pumps in the basement and shutting them off when the tank fills. A siphon at the top of the tank where the water is purest supplies water for the building's household needs. If the structure is equipped with sprinklers or standpipes supplying hallway or stairwell fire hoses, water for these systems is delivered through a drain in the tank's bottom.

The smallest tanks contain about 12 tons of water; larger ones are called on to hold considerably more. Although non-wood tanks have been constructed, cedar and redwood still outlast most other reasonably-priced materials. In addition, the pieces are easily transported to a roof for assembly.

Architects have contributed to the charm and character of the skyline by hiding many of these New York City water vats inside fanciful rooftop enclosures. A quick glance at The Manhattan Skyline Portraits reveals scores of these contrivances, along with less imaginative, utilitarian structures, many of which shelter elevator and ventilation machinery as well. Others proudly display their New York icon for all to see, even going so far as to decorate them. One SoHo building even sports a tank-shaped objet d' art on its formerly-vacant tank pedestal. Approximately 1,500 of Manhattan's water tanks are pictured in the two skyline panoramas. BACK TO QUESTION 1.

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MORE INFORMATION — QUESTION 3: The difference between a structure's built square footage and useable square footage can mean either the luxury penthouse or the bankruptcy doghouse for developers of commercial and residential real estate.

This gap becomes a particularly wide chasm to bridge in the case of the Empire State Building (and many of its statuesque brethren) because of an irrefutable law of skyscraper design. The higher you build, the more floor space gets gobbled up by utilities, particularly by elevators and emergency staircases.

The square footage devoted to an elevator not only affects the lobby where the ride begins, but is subtracted, floor after floor, from every story of rentable office space the elevator serves. The Empire State Building is packed with 76 of these floor-space omnivores. In fact, roughly 25 percent of each floor of the Empire State Building's slender tower is devoted to elevator shafts and access. Useable floor space is further eroded by the before-mentioned stairways, as well as by rest rooms, hallways, utility closets, ductwork, plumbing, and conduits for electrical and telecommunications lines.

111 Eighth Avenue by comparison is served by about half the number of elevators. Multiply that by just 17 floors, and the amount of floor space lost to these people movers is only about one sixth the space lost in the Empire State.

Other factors come into play to explain why 111 Eighth Avenue should be the new home of the Very Large Corporation of America. If you want to know even more, read on, or go on to Question 4.

A little history of both buildings will further explain this apparent paradox.

Sprawling over an entire city block of Chelsea like a beached whale, 111 Eighth Avenue originally was a giant warehouse for the Port of New York Authority. Officially dubbed the Commerce Building, it was also known as the Union Inland Terminal No. 1. It was completed in 1932, just a year after the then world's tallest skyscraper, the Empire State Building, opened for business.

Both structures enclosed enormous amounts of commercial space when completed, but in configurations that were very different.

Lusby Simpson, the architect of 111 Eighth Avenue, built property line to property line, stacking 17 floors, most of them larger than two football fields, one on top of the other. As most of the building was primarily warehouse space, human amenities were of little concern.

The Empire State Building by contrast had to be convenient and comfortable for thousands of office workers destined to use it. The firm of Shreve Lamb & Harmon started with half a block of valuable Midtown real estate and built upwards, 85 floors of rentable office space in all.

So how is it that 111 Eighth Avenue is the better buy for the Very Large Corporation of America? Putting it another way: Although 111 Eighth Avenue has a footprint twice the size of the Empire State Building, how can 111 Eighth Avenue offer more floor space if it's only one fifth as tall?

The key is a New York City zoning law passed in 1916 that requires setbacks for multistory structures whose footprint fully occupies the building lot. This measure was passed to prevent greedy developers from overbuilding a site, turning the street into a dark, airless canyon. A complex formula was created so designers can calculate the required frequency and size of those setbacks. Generally speaking, the taller the structure, the more architects have to push the walls away from the sidewalks to let sunlight reach street level.

Although this zoning law applied to both buildings in our example, its provisions were far more restrictive on the Empire State Building designers. For instance, the square footage of each story between the 30th and 71st floors is only 30 percent the floor space of the first five stories, a 70 percent reduction. The effect is a slender tower resting atop a wedding-cake-like base, an elegant profile and commodious to street life, but murder on the total rentable space.

Another consideration was the necessity to limit floor size so that each office had at least one exterior wall with a window for illumination and ventilation. This was essential in the days before fluorescent lighting and air conditioning. In fact, pencil-thin skyscrapers were the norm of pre-Depression New York primarily for this reason. Compare those towers to the steroidal, hermetically-sealed, air-conditioned skyscrapers possible in the last half of the 20th Century.

The crates of goods stored in the Port Authority's warehouse needed little illumination and ventilation. Today's office workers using these same floors can do so thanks to modular office equipment, modern ventilation systems, effective artificial lighting, and the relatively cheap energy that makes these vast spaces habitable. BACK TO QUESTION 3.

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