How Do Rooftop Water Tanks Work? Why You May Still Need a Booster with Rooftop Water Storage

You can’t see a panoramic photo or aerial tour of New York City’s rooftops without noticing the thousands of water tanks above many buildings, particularly those built prior to World War II. If you’ve wondered, “How do rooftop water tanks work?” this post explains their function. We also review why sometimes booster pumps are needed even with rooftop water storage, so you understand more about how to achieve the perfect water pressure in your condo or co-op building.

How Do Rooftop Water Tanks Work?

Water storage explained

The invention of the elevator meant that New York City buildings could finally reach above six or seven stories – the limit most people would climb using stairs to their residence. But taller building heights came with a new problem: how to provide water for the upper stories. Supplying water to towers and skyscrapers involves pushing against the force of gravity.

Water circulator pumps can only do so much to counteract the natural gravitational force. In fact, for every foot that water moves upwards, it loses 0.434 psi. That means that the upper stories on super tall buildings have trouble getting any water at all. This isn’t just an issue of convenience. Low water pressure spells disaster for fire suppression systems like sprinklers.

To overcome this pressure issue, high buildings in New York City started adding water tanks to their rooftops. These tanks could store enormous amounts of water to be released over time as needed to upper floors, while the municipal water supply took care of lower stories directly. A pump station in the basement propels water to the roof for use later. As the tank empties, it triggers the pump to send more water from the city main to the roof.

You’ll observe that rooftop water tanks in New York City are only made of two materials according to the building code: steel and wood, with cedar wood being the preferred choice. It’s a natural insulator, keeping water cool in summer and preventing it from freezing in winter. The first builders of early rooftop tanks were coopers, immigrant barrel makers who learned their trade in Europe, and the current makers of wooden rooftop water containers in New York are descendants of those family businesses.

Although the materials and construction of rooftop tanks haven’t changed in over a century, new technology has been added to monitor water levels, temperatures, and the like. New York City requires annual tank inspections, as well as yearly draining and cleaning to prevent the growth of dangerous bacteria and other contaminants. This work must be done by licensed master plumbers with confined space training.

With proper maintenance, rooftop tanks can last decades. When they’re replaced, it’s done all in one day, like assembling a giant wine barrel, with no glue involved.

Some of the factors involved in installing rooftop water tanks include:

• Making certain the roof can hold the weight of the tank and water
• Securing the tank against natural elements, especially wind, which affect all rooftop equipment
• Protecting the water supply against contaminants, animals, etc.
• Allowing access for maintenance, inspection, and repair
• Creating a conduit for overflow
• Ensuring the basement pump system is sufficient for tank supply
• Designing correct circulation from the tank to units

Why Do Rooftop Storage Tanks Still Often Require Booster Pumps?

Fighting gravity at upper levels

As mentioned above, a ground-level pump system is still needed with rooftop water tanks to supply them with water in the first place. These heavy-duty pumps are similar to the booster pumps we use in newer tall buildings that rely solely on the New York City municipal pipes. Booster pumps give extra “oomph” to water pressure, helping plumbing systems overcome the force of gravity to ensure equal water pressure on all floors and ensuring fire suppression systems have adequate water supply.

However, even with a rooftop water storage tank, you may need an additional booster pump or series of booster pumps plus the basement pump. Why? You still have to consider the force of gravity with rooftop tanks. Water wants to follow its natural flow downwards from these tanks, meaning lower floors may still wind up with higher water pressure than upper ones, especially the first few floors beneath the tank.

While simply having any water at all may have been enough for early NYC tall building dwellers, nowadays the demand for perfect water supply is more exacting, and fire codes have also become stricter, measuring precise sprinkler pressure during inspections.

When our experts at Antler Pumps work with clients in New York City tall buildings that use booster pumps, both with and without rooftop water tanks, we use a variety of factors to calculate and achieve ideal water pressure. These include peak demand loads, height of the building, pressure at the municipal supply, plumbing anatomy (e.g., presence of or ability to add risers), operational issues, and budget.

Sometimes we add pressure reduction valves at lower levels to eliminate high static pressure and excessive noise at taps. In newer buildings where space allows, we may suggest using multiple interior steel water storage tanks spaced at certain intervals, each with their own booster pumps, rather than a single rooftop tank. Each property has to have the water pressure system customized for its unique features.

Is your property experiencing water pressure problems? Whether you have a rooftop water tank or use only the municipal water supply direct from the main, you likely need the assistance of pumps to get that perfect pressure occupants crave. We welcome the opportunity to consult with you on your pressure issues. Call Antler Pumps today at 212-534-2500 to set up an appointment.