You see them all the time, rising above our communities. Perhaps you had even climbed one when you were younger. But have you ever wondered how water towers work? Why do you need the water to be in the sky? It sounds like a waste of time, doesn’t it? I wanted to give a basic rundown of their operations and what they are for.
Water towers are the best low-tech answer for providing water pressure. With few to no working parts, little can go wrong in providing the public with 24-hour, consistent water pressure. Without water towers, a utility would need a constantly running pump that could adjust to current demands on the fly. That’s not very economical. In most cases, it’s impractical.
So why pump it in the air? Every 2.31 feet a column of water has in elevation equals one psi. It doesn’t matter how wide the column is. It can be the size of a straw or 20 feet in diameter. The elevation is what matters. So if you put the column 140 feet in the air, you get 60 psi. 140/2.31=60.61 psi What would that be in metric?
Most water systems operate from 30 up to 80 psi. Ideally, they run between 60 and 70 psi, Depending on how high the water tower is above your faucet. Pressure is the only reason the towers are in the air. So why not just put a small pipe in the air and leave it that? Why have a large tank at the top?
Water Tower Storage
Without the tank, the pumps would still have to run constantly. The pipe would empty as soon as the pump kicked off. Having a tank on top allows for more volume. Booster pumps run just long enough to fill the tank then they shut off. Gravity does the rest.
Storing water in the air also serves as an emergency backup. If the electricity goes off, you will still have water for several hours, up to a day. In fact, most municipalities hold at least 24 hours’ worth of water in their towers. They come in all shapes and sizes for this reason. The more customers they have, the more volume they need in storage.
Another reason to have ample storage ready to go on demand is for fire protection. Pumper trucks can suck a lot of water out of a distribution system very quickly. If you have a large fire and several trucks hooked up to fire hydrants, they could suck the water out of the lines faster than the pumps could keep up. Having those reserves in storage alleviates this problem by helping with demand along with the pumps.
FIFO vs LIFO vs Mixed Water Towers
The diagram above shows a LIFO model. While outdated, it is the simplest to demonstrate. LIFO stands for Last In – First Out. The last bit of water to enter the tank while the pumps run is the first to leave after they shut off. This setup can be problematic as you will end up with stagnant water at the top of the tank. It will keep pressure on the system, but if the tank level drops, that stagnant water will enter the distribution system on its way to your house.
FIFO water towers do the opposite. As demonstrated below, the first water that entered the tank will be the first to leave the tank. This is a much better approach.
Mixed water towers do just as the name suggests; they mix the water, so it doesn’t become stagnant. This method is commonly used to retrofit older water towers with only one standpipe. It’s achieved by installing an agitator into the tank to mix the water, so it doesn’t become stagnant.
Water Tower Vents
Have you ever put your finger over the end of a straw and tried to blow into it? Yeah, it doesn’t work so well. If towers did not have vents, the same thing would happen. It’s a vital component of the tower because the tank is useless without it. Venting allows the water to displace the air in the tank preventing a vacuum. If you were to block the vents as the tank drains, it could collapse.
But having the water exposed to the open air has its own challenges. So a fine mesh is installed over the openings to keep out bugs and birds. They are typically faced downwards to keep the rain out and birds from defecating into the tank.
Overflows are also very important. If your pump controls malfunction, water could be forced out of the vent at the top of the tank. This could damage the mesh screen or even the vent housing itself. So an overflow pipe just below the vent allows the tank to overflow safely. The overflow lets the operator occasionally overfill the tank to push out any floating debris or stagnant water, especially if you have a LIFO setup.
Keeping water towers clean
The paint job on a water tower is also vital to its operation. If the exterior paint gets too thin, rust could take hold. The paint protects the metal inside from the often chlorinated water. A small chip in the paint on the interior could cause severe rusting very quickly. Metal and Chlorine do not play well with each other.
Cleaning of water towers should be performed periodically as routine maintenance. Iron and sand that make their way through the treatment process build up in the tank, and while not harmful to the public, they can make the water cloudy if it makes its way out of the tank. Optimally tanks need to be cleaned out annually. But it should go at most five years between cleanings.
Tanks need a new coat of paint when it gets too thin. Painting is the costliest part of operating a water tower. Having worked with several small municipalities, I know this is a significant concern. Getting a small water district to spend thousands of dollars for a paint job can take time and effort. But this should be included in any annual budget for tank maintenance.
Forty years ago, it was common to see teenagers climbing the local water tower. Swimming in the tanks wasn’t unheard of either. Today security is taken much more seriously by municipalities. Having someone swimming in your drinking water isn’t something people will or should tolerate. That’s why ladder guards and fences are typically present around most water facilities. After 9/11, terrorism had the whole nation worried about safe drinking water. It is now a felony to climb a water tower without consent today.
Water towers are silent work horses
If you came here because you were curious about water towers, I hope you have a slightly better understanding of their inner workings. The next time you pass a tower, I hope you will appreciate what a marvel they are. They tend to blend into the background because they are so commonplace. They are silent workhorses that have allowed us to grow as a society. That’s basically how water towers work.
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