Clean water is one of humanity’s most fundamental
needs, and those of us who live in urban areas usually get our water from some kind of centralized
public system. Operating a water system is a major responsibility
that has implications for public health and safety. In dense urban areas, a clean and abundant
supply of water is an absolute necessity, not just for drinking, but also for sanitation
and firefighting. And it’s not just something we need every
so often; water is a constant necessity both day and night, on weekends, holidays, and
any time in between. So, the job of finding enough water, making
it safe to use, and then reliably distributing it to the system customers with almost no
downtime is a monumental task that requires a lot of infrastructure. And probably the most visible component of
a public water system is the elevated storage tank, also known as a water tower. I’m Grady and this is Public Works, my video
series on infrastructure and the humanmade world around us. [This video is sponsored by Bombas. More on that later.] Let’s say you’re the owner of a public
water system. You’ve found a source of water of sufficient
quantity for your customers, you’ve found a way to clean that water so it’s safe for
them to use, and now it’s time to send the water on its way. There are a few ways we can get water from
one place to another. One of them is just to carry it there. Whether it’s on the back of an animal, on
a truck, or a bottle in your backpack, we still physically carry water all the time. But it’s usually not the most efficient
way. The first infrastructure dedicated to water
conveyance was the open channel. Whether in a ditch, canal, or aqueduct, the
water is carried by gravity, sometimes over very long distances. We still use open channels to carry water
for irrigation and drainage, but they have some disadvantages as well. The water is exposed to pollution and contamination,
channels bisect the land, making it difficult to get across, and the water can only flow
to areas of lower elevation than where it started. And that last one is a big disadvantage, especially
if you’re trying to deliver water to an area with hills or mountains. So most public water systems today rely on
pipes for distribution. Simply putting a top on an open channel allows
us to take advantage of pressure to move fluids where we want them to go. Just like electrons in a wire flow from high
to low voltage, a fluid in a pipe will flow from high to lower pressure. So, if you raise the pressure at one end of
a pipe, you can send your clean water to anywhere you want it to go. And how do you raise the pressure of water? With a pump. A pump is a device that moves fluids. In some cases a pump literally lifts the fluid
to a higher elevation, but in most cases a pump imparts energy to a fluid by raising
its pressure. And pumps, especially the size of pumps that
serve entire cities, are expensive. So if you’re tasked with choosing the size
of the pump you need for your public water system, what do you do? Maybe you measure the amount of water that
the city uses in a given day and select a pump that can match that flow rate. Let’s see how that would work. It’s midnight in your city and most of your
water customers are asleep. Besides the industrial customers that run
24/7, water demands are minimal, and your pump is having no trouble meeting them. But around 5 am, automated sprinkler systems
start kicking in. Around 6 am, people start waking up, taking
showers, brushing their teeth, cooking breakfast, all things that require water. It doesn’t take long before the water demand
exceeds the capacity of your pump. Almost right off the bat, your new pump can’t
meet your system demand, because it was only sized for the average. Water demand in large urban areas can vary
significantly over the course of a normal day, with the peak hourly demand (usually
in the morning or evening) sometimes being as much as 5 times the average daily demand. So, if you are trying to meet your customer’s
water needs using just pumps, instead of just one, you might need as many as five pumps
(or one huge pump that can do the work of 5). And not only that, you’ll have to be constantly
cycling the pumps on and off to meet the variable demand, increasing the wear and tear on your
equipment. And here is where storage comes in. Let’s add a water tower to the system and
try this experiment again. It’s midnight and demand is low, but your
pump is running full wide open. Instead of water flowing customers, it’s
flowing into your water tower, filling the tank slowly but surely. As morning comes and demand starts to increase,
your pump continues running. It’s not able to meet the demand on its
own, but the stored water in the tank is making up the difference. All your customers are getting the water they
need. As people start their day, demand again drops
below average. But, the pump keeps running and the extra
flow goes into the tank. Demand again begins to spike as the residents
of the city start cooking dinner, taking baths, and watering the plants. All this extra water use drains the tank again
before most people go to bed and the cycle starts again. It’s pretty easy to see how storage makes
your water system more efficient. It smooths out the peaks and valleys of water
demand not just on your pumps but all your upstream infrastructure, including your water
treatment plant and raw water supply. Without storage, all those facilities would
need to be sized for peak demand, increasing their cost. With enough storage, pumps and other infrastructure
can be sized for average demands, saving not only cost, but also complexity, because you
don’t have to predict changes in demand and respond accordingly. Sometimes those peaks and valleys are predictable,
but sometimes they’re not. Some of the biggest water demands in urban
areas are from fires. Without a firefighting force and enough water
to supply them, fires can burn out of control in dense urban areas. In fact, many of the deadliest disasters in
history were fires in cities before modern water systems. Now most municipalities and building codes
have minimum requirements for the amount of water that must be available to firefighters. And having water stored and ready, like in
a water tower, goes a long way to being able to respond to an emergency. You may thinking, c’mon Grady. This is nothing new. Storage is the age-old solution to any situation
where the supply doesn’t match the demand. And, yeah, it might not be anything remarkable
to store water in a big tank. But water towers aren’t just big tanks,
they’re big tanks elevated above the ground. And that’s because water towers aren’t
just storing water; they’re also storing energy. Water distribution systems rely on pressure
to get the water where it’s going. If you’ve ever taken a shower with low water
pressure, you know how frustrating it can be, because you just can’t get enough water
out of tap. Pressurizing a water system is also important
for public health. Without enough pressure in the pipes, contaminants
could make their way into the system through taps or small leaks. Most water systems get their pressure from
pumps, and it takes a lot of energy to maintain this pressure. So, having the ability to store not only the
water itself, but also the energy that has been imparted to it by the pumps is important. In some areas, where electricity costs vary
based on demand, you can run the pumps at night when electricity is cheap to fill up
your water tower. Then, leave the pumps off during the day when
electricity is more expensive, allowing just the tower to pressurize the system and serve
your customers. Storing energy this way is also carried out
at a larger scale to help with electrical grid reliability, but that’s a topic for
another video. Elevated storage is also beneficial during
a power outage, by keeping the system pressurized even when pumps are out of service. But how elevated do they need to be? You might know that the pressure within a
body of water is related to the depth. The deeper you go, the greater the pressure. Just like in a pool or the ocean, a water
distribution system has the same relationship between depth and pressure. It just happens to be confined within a series
of pipes. So, you can imagine a water distribution system
as a virtual ocean under which we all live, and the water surface in elevated storage
tanks represents the surface of the virtual ocean. Imagining a water system this way makes it
easy to see the challenge of delivering water to customers at the right pressure. If our cities were flat, this would be pretty
simple. All the buildings would sit at the same depth
in the virtual ocean. But most areas have at least some amount of
topographic relief. Customers at low elevations are at the bottom
of the virtual ocean, where pressures can be too high. You might think this is a good thing, but
plumbing pipes and appliances are only rated to certain pressures, so exceeding those ratings
can cause serious damage. Sometimes buildings at low elevations will
be equipped with special valves to reduce the pressure. Customers at high elevations will be near
the surface of the virtual ocean, having very low water pressure. As I mentioned, this can be not only frustrating,
but also lead to contamination of the system. To solve this challenge, many large cities
maintain separate distribution systems called pressure zones, each with their own water
tower, to serve customers at different elevations within the city. But, what happens if you need to serve customers
at different elevations in the same location? Tall buildings, like skyscrapers, can have
adequate water pressure on the lower floors, while the higher floors can go up near the
surface or even above the virtual ocean in the water distribution system. So, instead of relying on city water pressure,
most tall buildings use their own pumps to provide water to the upper floors. And some cities, like New York, even require
that each building have its own elevated storage tank. Not every city uses water towers. Some have their entire water supply at a higher
elevation, minimizing the need to add pressure to the system. And, sometimes it just makes more sense to
rely on pumps alone to keep the system up and running. After all, water towers aren’t cheap, they
take up quite a bit of space, and they can allow water to stagnate if it isn’t circulated
enough. But, with public water supplies, reliability
is key. And, it’s been a long time since gravity
was knocked offline from a thunderstorm, so elevated storage tanks (in some form or fashion)
are definitely here to stay. Thank you for watching, and let me know what
you think! Thanks to Bombas for supporting Practical
Engineering. I’ll be honest, I’ve don’t usually put
a lot of thought into the socks I wear. But, Bombas does. They’ve put a ton of research, development,
and even some practical engineering into their socks. I’ve been wearing Bombas for a while now,
and I can easily say they are the most comfortable and well-designed socks I’ve ever owned. Bombas motto is “Bee Better” and that’s
because for every pair of socks you buy, they donate a pair to someone in need. Socks are the number one requested item at
homeless shelters, and I love this one-for-one business model. Support Practical Engineering by using code
PRACTICAL at bombas.com. Get a 20% off a pair for yourself, or they
make awesome gifts. Either way, you know that someone in need
will be getting a pair too. Again, thank you for watching, and let me
know what you think!
I love practical engineering. One of my favourite YouTube channels.
If anyone has other questions about water networks after this vid, feel free to ask. I work as a controller for a water company so send water around the network, get pumps turned on off etc.
Another utility person here. IMO, they fail to mention most large utilities are demolishing their elevated storage tanks. its so much easier to install variable frequency drives on pumps. To boot, my state and probably every other state requires standby power for water distribution pump stations so there is no issue with loss of power. Elevated storage tanks are crazy expensive to maintain. Painting costs like 150k every 5-10 years. They also need cathodic protection and inspection by diver nearly every year. Ground storage tanks, pumps and VFDs are so much better and cheaper to operate.
So much padding, it's like a university essay where they've finished filling only half the the word count.
I see a video from Practical Engineering, I upvote.
There ain’t no rules on the water tower
Simcity 2000 taught me this.
This man has a dark side. I don't know what he does when nobody is watching but it's not a good thing. I'm on to you Grady, you are hiding something.
This video is perfect length and has the perfect amount of explanation. Anyone who thinks the video is running too long didn't appreciate a lot of the subtle and interesting points touched on in the video. The fact that water tower can be used to even out variable demand is not trivial at all. They are like capacitors in an electric circuit! And the lack of an equivalent storage system in the power market to meet variable demand has significant financial ramifications.