Water Towers
How Water
Towers Work
Have you ever experienced a "water failure"? That is, have you ever turned on your faucet and found that no water came out of it?
If you get your water from a
municipal water system, the answer is probably "no."
We have power failures
all the time. Cable TV goes out fairly frequently.
Although less common, the
phone system goes down every so often, and it is now common to get an
"all circuits busy" message when making long-distance calls.
But the water in any city or
suburb is always there. Water pressure is very reliable.
A big reason for that level
of reliability is the water tower.
You see water towers
everywhere, especially if you live in a flat area full of small towns.
Each water system has one or
more towers.
In this article, we will look
at how water towers work. The next time you drive by a water tower, you will
know exactly what it is doing.
Tower, Tank and Pump
A
water tower is an incredibly simple device.
Although water towers come in
all shapes and sizes, they all do the same thing: A water tower is simply a
large, elevated tank of water.
For example, take the water
tower shown at the right. This tower is located in Kill Devils Hill, near Kitty
Hawk, NC. It is about 165 feet (50 meters) tall.
Water towers are tall to
provide pressure. Each foot of height provides 0.43 PSI (pounds per
square Inch) of pressure.
A typical municipal water
supply runs at between 50 and 100 PSI (major appliances require at least 20 to
30 PSI).
The water tower must be tall
enough to supply that level of pressure to all of the houses and businesses in
the area of the tower.
So water towers are typically
located on high ground, and they are tall enough to provide the
necessary pressure.
In hilly regions, a tower can
sometimes be replaced by a simple tank located on the highest hill in the area.
A water tower's tank is
normally quite large.
A normal in-ground swimming
pool in someone's backyard might hold something like 20,000 or 30,000 gallons
(that's a lot of water!), and a typical water tower might hold 50 times that
amount!
Typically, a water tower's
tank is sized to hold about a day's worth of water for the community served by
the tower.
If the pumps fail (for
example, during a power failure), the water tower holds enough water to keep
things flowing for about a day.
One of the big advantages of
a water tower is that it lets a municipality size its pumps for average rather
than peak demand. That can save a community a lot of money.
Say that the water
consumption for a pumping station averages 500 gallons of water per
minute (or 720,000 gallons over the course of a day).
There will be times during
the day when water consumption is much greater than 500 gallons per minute.
For example, in the morning,
lots of people wake up at about the same time (say 7:00 a.m.) to go to work.
They go to the bathroom, take
a shower, brush their teeth, etc.
Water demand might peak at
2,000 gallons per minute at 7 a.m. -- there is a big cost difference between a
500-gallon-per-minute pump and a 2,000-gallon-per-minute pump.
Because of the water tower,
the municipality can purchase a 500-gallon-per-minute pump and let the water
tower handle the peak demand.
At night, when demand
normally falls to practically zero, the pump can make up the difference and
refill the water tower.
In most towns, the water
people drink comes from either a well, a river or a reservoir (normally a local
lake).
The water is treated in
a water treatment plant to remove sediment (by filtration
and/or settling) and bacteria (typically with ozone, ultraviolet light and
chlorine).
The output from the water
treatment plant is clear, germ-free water.
A high-lift pump pressurizes
the water and sends it to the water system's primary feeder pipes.
The water tower is attached
to the primary feeders quite simply, as shown in this diagram:
If the pump is producing more
water than the water system needs, the excess flows
automatically into the tank.
If the community is demanding
more water than the pump can supply, then water flows out of the tank to meet
the need.
Form and Function
Water
towers come in all shapes and sizes.
Take, for example, this giant
peach along I-85 in Gaffney, South Carolina.
Water towers on top of buildings are a common feature in many
cities.
In a
city, tall buildings often need to solve their own water pressure
problems.
Because the buildings are so
tall, they often exceed the height that the city's water pressure can handle.
So a tall building will have
its own pumps and its own water towers.
In the following picture,
taken from the Empire State Building in New York City, there are at least 30
small water towers visible on the tops of these buildings.
Another interesting fact
about water towers -- they can affect your insurance rates!
During a fire, the water
demand increases significantly and may greatly exceed the capacity of the pumps
at the water plant.
A water tower guarantees that
there will be enough pressure to keep water flowing through the fire hydrants.
Fire insurance rates are
normally lower in a community in which the water system has water towers.
The next time you are out
driving around, especially if you are driving through a series of small towns,
take the time to notice the water towers.
Now that you know how they
work, you will be amazed by how many you see and by all the different forms
they take!
FUN WATER TOWER
FACT
For
pilots of small, private aircraft, water towers are a huge help because:
·
They are large.
·
They are elevated, making them easy to see from an airplane.
·
All small towns have them.
·
Small towns are nice enough to paint the town's name on nearly
every tower!
If you have ever been in a
small airplane flying cross-country, you know that from the air, all small
towns look the same; it is very easy to get confused.
When you don't have a GPS
receiver, water towers make navigation a LOT easier!
Marshall Brain,
Founder
Marshall Brain is the founder of HowStuffWorks. He holds a bachelor's degree in electrical engineering from Rensselaer Polytechnic Institute and a master's degree in computer science from North Carolina State University. Before founding HowStuffWorks, Marshall taught in the computer science department at NCSU and ran a software training and consulting company. Learn more at his site.
Marshall Brain is the founder of HowStuffWorks. He holds a bachelor's degree in electrical engineering from Rensselaer Polytechnic Institute and a master's degree in computer science from North Carolina State University. Before founding HowStuffWorks, Marshall taught in the computer science department at NCSU and ran a software training and consulting company. Learn more at his site.
