By Dr. Brian Blodgett
Faculty Member, Homeland Security, American Public University
This is the first of a two-part series on the vital role water storage facilities play in our national security.
Americans take having safe water for granted. Unlike electric power or phone service, the local water utility rarely fails, even during power outages. At APU, I teach my students in the Homeland Security course on critical infrastructures just how vital water is not only for drinking and cooking, but for so many other uses.
By understanding the role that water tanks play in the system, we must also understand how some of the ways that our water systems can fail, which include poor maintenance and damage to the water tanks.
The Water and Wastewater Systems Sector Is One of Four Lifeline Sectors
As one of our nation’s critical infrastructures, the Water and Wastewater Systems Sector is one of four lifeline sectors, the others being communications, energy, and transportation.
One vital aspect of this sector are the storage tanks that supply water to our homes, schools, offices and public places. In this two-part series we’ll examine this critical aspect of our nation’s water and wastewater infrastructure, one we use every day without being aware of how important water tanks and towers are until we are faced with a water shortage or, worse, no water at all.
We often see water storage tanks with the name of a town, manufacturing company, factory or just a novel paint design. But their primary purpose is not advertising. Water tanks actually have two primary purposes: storage of water for distribution and providing sufficient pressure for the city’s water system.
Types of Water Towers
A water tower is the most iconic symbol of a municipal water system. It is, in the most basic terms, an elevated storage tank. These tanks are often constructed of bolted, riveted, or welded steel, but many are made of wood and are common throughout the United States.
The basic configurations for these elevated tanks are leg or supported tanks, single pedestal tanks and fluted pillar/hydropillar.
Leg or supported elevated tanks have four or more legs and braces with a central insulated riser pipe through which water enters and leaves the tank. These tanks are very stable because of their multiple leg design. The access ladder is normally on the outside of one of the legs or within the central pipe.
Single pedestal tanks have only one support structure in the center of the tank with a large volume tank at the top. The pedestal tank is both easier and less expensive to maintain than the leg support tanks, but is the most expensive to construct. The access ladder and the riser pipe are both within the pedestal tube.
Fluted pillar/hydropillar elevated tanks have a large, overhead water storage container. Within the fluted shaft, there is room for storage, meeting rooms, offices, or equipment and machine storage. The access ladder is inside the shaft and can also be a flight of stairs.
Planners Need to Carefully Assess a Community’s Water Needs
The amount of water a city needs is not random. Practicality means that a city must have enough water stored that is equal to at least the daily amount of water used, which can vary by season; summer normally requires more water than winter.
Likewise, the amount used varies during the season based on various factors, but the most common variations are temperature and lack of rainfall. Therefore, planners need to carefully assess the amount of water needed based not on just one day of high usage, but rather on an extended period of high temperatures.
While water in the tanks does not normally freeze because it circulates, freezing can still occur in extremely cold weather, especially if the region is not accustomed to very low temperatures. If the tanks do not have enough insulation and there is a lower than normal demand, that results in less water circulation.
If the greatest amount of water used is in the winter, there is a possibility that some of the water, perhaps a foot or two, might freeze. If so, municipal officials might consider that a larger tank is necessary.
Ice inside a water tower not only limits the available amount of potable water, but it is also dangerous. Ice sloshing around in the tank can rupture a wall. An extreme cold spell followed by strong winds provide favorable conditions for this rupture to occur.
Another consideration for water tower construction is if the city is likely to grow measurably in population, commerce and industry. City planners need to take this possibility into account.
Lastly, but of extreme importance, is how much water the local fire department needs for fire prevention. For most towns, one tower may be enough; however, larger cities might have multiple million-gallon water towers.
Water Storage Towers and Their Height
A standard water tower holds from 50,000 to 2 million gallons. For example, the North Wales Water Authority, knowing that it needed a massive water tank not only for the existing community, but also for the growing demand, commissioned the largest water tower in the world. This massive water tower is located in Chalfort, Pennsylvania, north of Philadelphia, and holds 4.1 million gallons of water.
Water towers tend to be roughly the same height — around 165 feet. This height is not due to engineering factors relating to the weight of the water, but rather because of the need to elevate the flow of the water.
When water enters our homes through the city’s water pipes, we expect it not to trickle or to blast through the tap. The typical home water pressure is about 50 pounds per square inch (psi); anything below 40 psi is too low and water pressure above 80 psi can result in broken water pipes. Since high water pressure also stresses the plumbing system, many cities require pressure reducing valves if the water pressure is over 65 psi.
Water, like all gases, liquids, and solids, has weight as a result of Earth’s gravitational forces. Water weighs 62.4 pounds per cubic foot. The weight of a cube of water one-inch square and one foot in height is 0.4333 pounds. If 100 of these cubes of water were stacked one on top of each other, the pressure on the bottom one-square-inch cube of water would be 43.33 pounds of pressure per square inch, regardless of the diameter of the pipe holding the water.
Keeping this factor in mind, an elevated water tower 100 feet high would have a water pressure of slightly more than 43 psi, which is too low. But a water tower that is 165 feet high results in a water pressure of about 71 psi. While this is more water pressure than the average home has, the water needs to flow at this pressure to ensure that all homes and all floors are served sufficiently.
Water towers can be less than 165 feet high if they are located on hills or can be taller if there are likely to be multi-story buildings that may require additional water pressure. However, multi-story buildings require a pump or a rooftop tank to increase water flow so it is even throughout a building.
As to which water tower is the tallest in the United States, it depends. If you are a purist, the tallest sphere is the Union Watersphere in Union, New Jersey, at 212 feet. The tallest spheroid is in Edmond, Oklahoma, and it measures 219 feet.
However, both are dwarfed by Cape Canaveral’s Blue Origin’s leg supported water tower at 351 feet tall. This massive tower stores hundreds of thousands of gallons of water for the space launch complex.
In Part II, we will discuss ground storage tanks, standpipe storage tanks, pumping stations, rooftop water tanks, maintenance and damage to water tanks.
About the Author
Dr. Brian Blodgett is an alumnus of American Military University who graduated in 2000 with a master of arts in military studies and concentrated land warfare. He retired from the U.S. Army in 2006 as a Chief Warrant Officer after serving over 20 years, first as an infantryman and then as an intelligence analyst. He is a 2003 graduate of the Joint Military Intelligence College where he earned a master of science in strategic intelligence with a concentration in South Asia. He graduated from Northcentral University in 2008, earning a doctorate in philosophy in business administration with a specialization in homeland security.
Dr. Blodgett has been a part-time faculty member, a full-time faculty member and a program director. He is currently a full-time faculty member in the School of Security and Global Studies and teaches homeland security and security management courses.
