08 Water Treatment and Distribution

Summary

This script delves into the intricate world of water supply systems, exploring the journey from raw water collection to purification at treatment plants. It discusses the challenges of contamination and the crucial role of environmental engineers in ensuring water safety. The script also highlights the mechanics of water distribution, the importance of water towers, and the complexities of maintaining water pressure in a network that serves both residential and commercial needs.

Takeaways

• 💧 The script discusses the journey of water from its collection in a watershed to its treatment and distribution for various uses, including drinking, cooking, and industrial purposes.
• 🌿 It highlights the presence of contaminants in raw water, such as microorganisms, dissolved salts, metals, and organic chemicals, which necessitate treatment before the water is safe for consumption.
• 🚰 The importance of environmental engineers and scientists in designing, building, and operating water treatment facilities is underscored, emphasizing their role in ensuring water safety and quality.
• 🛠️ The script outlines the water treatment process, which includes clarification, filtration, and disinfection, to remove impurities and contaminants from the water.
• 🌱 It explains the challenges of managing water quality in reservoirs, such as controlling algae growth and preventing anoxia, which can deplete dissolved oxygen levels and harm aquatic life.
• 🌊 The role of the Safe Drinking Water Act and the Environmental Protection Agency (EPA) in regulating water quality and setting standards for public water systems in the US is mentioned.
• 🏭 The script touches on the impact of human activities on water contamination, including industrial discharges, agricultural runoff, and improper disposal of chemicals and waste.
• 🌐 It describes the water distribution system, which operates under pressure and includes water mains, service lines, valves, and water towers to manage demand and ensure continuous supply.
• 🏢 Desalination is presented as a significant process for converting seawater into drinking water, especially in areas with limited freshwater resources, despite its higher energy and cost demands.
• 🔄 The script emphasizes the efficiency and robustness of the water distribution system, which includes backup power systems and the use of interconnected loops to prevent service disruptions.
• 🏠 The private component of the water distribution system is also discussed, detailing the service line, curb valve, water meter, and interior shut off valve in residential settings.

Q & A

What is the primary purpose of collecting raw water?

The primary purpose of collecting raw water is to supply it to municipalities for various uses including drinking, cooking, personal hygiene, washing clothes and dishes, circulating heat through homes, watering lawns, and a wide array of commercial and industrial purposes.

Why is raw water not safe for human consumption immediately after collection?

Raw water is not safe for human consumption immediately after collection because it contains various contaminants, some of which can be extremely hazardous to human health, such as microorganisms, dissolved salts and metals, inorganic and organic chemicals, and even radioactive particles.

What are some natural sources of water contamination?

Natural sources of water contamination include microorganisms like Legionella bacteria found naturally in the environment, arsenic, lead, mercury, and radioactive particles originating from the erosion of natural deposits, and calcium and magnesium dissolved into groundwater as it percolates through certain geologic formations.

How does human activity contribute to the contamination of raw water?

Human activity contributes to water contamination through the discharge of dangerous pathogens from human and animal feces, industrial pollutants from facilities like refineries and chemical plants, cadmium from the corrosion of galvanized steel pipes, nitrates from agricultural land and residential yards, and organic chemical contamination from the use of herbicides and insecticides.

What is the role of the Environmental Protection Agency (EPA) in regulating water quality in the US?

The EPA has the primary responsibility for regulating water quality under the Safe Drinking Water Act of 1974. It sets and enforces maximum permissible levels for over 80 possible contaminants and specifies the treatment processes required for all public water systems.

What is the main function of environmental engineers in the context of water treatment?

Environmental engineers design, build, and operate water treatment facilities and processes consistent with the given community's needs and available water resources. They work closely with environmental scientists and chemists to develop protocols and technologies for testing water contamination accurately.

What are the three basic functions performed by a water treatment plant?

The three basic functions performed by a water treatment plant are clarification, filtration, and disinfection.

How does the process of coagulation contribute to water clarification?

Coagulation contributes to water clarification by neutralizing the electrical charges that cause suspended particles in the water to repel each other. A coagulant, such as Alum, is added and causes these particles to cling together, forming larger clumps called flocs, which then settle to the bottom of the basin.

What is the purpose of a water tower in the water distribution system?

A water tower serves as an intermediate storage facility in the water distribution system. It helps maintain an appropriate level of pressure throughout the system, provides additional pressure during peak demand, and ensures continuity of water supply in case of power failures.

What is the significance of water main loops in the water distribution network?

Water main loops are significant because they allow water to flow through a main in either direction, ensuring that the system can be easily isolated for maintenance and repair without disrupting the water supply to a large number of homes.

How does the water distribution system ensure water is delivered at the right pressure to consumers?

The water distribution system ensures water is delivered at the right pressure to consumers by using a combination of pumping stations and water towers. The system operates under pressure, and the water tower supplements the pump during peak demand, maintaining the necessary pressure for water delivery.

What is the process of desalination and why is it becoming more popular?

Desalination is the process of converting seawater into drinking water, typically using technologies like reverse osmosis to remove salt from seawater by forcing it through a membrane under pressure. It is becoming more popular due to technological advances that have reduced the cost and increased the efficiency of desalination plants, making it a viable solution for areas with limited freshwater resources.

Outlines

00:00

💧 Water Supply Contamination and Treatment Overview

This paragraph discusses the various sources of raw water and the contaminants they may carry, including microorganisms, dissolved salts, metals, and organic chemicals. It highlights that while some sources like upland springs might provide potable water, most require treatment due to hazardous contaminants. The paragraph also touches on the natural and human-caused origins of these contaminants, such as industrial discharges and agricultural runoff. It emphasizes the role of the Environmental Protection Agency (EPA) in regulating water quality and setting treatment standards for public water systems, which are adapted by environmental engineers to suit local needs.

05:01

🌱 Water Treatment and Environmental Engineering

The focus shifts to the role of environmental engineers and scientists in designing water treatment processes. It explains the preliminary steps of water purification that occur before the water reaches the treatment plant, such as managing algae blooms in reservoirs and maintaining dissolved oxygen levels to prevent anoxia. The paragraph details the water treatment process involving coagulation, flocculation, sedimentation, and filtration, using alum as an example of a coagulant. It also mentions alternative disinfection methods like UV light or ozone, concluding with the importance of holding tanks in the treatment process.

10:05

🏭 Desalination and Water Distribution Systems

This section introduces the process of desalination, which is becoming increasingly important due to technological advances like reverse osmosis. It discusses the energy intensity and cost of desalination compared to traditional water treatment and highlights regions where it is a critical water source. The paragraph then describes the water distribution system, emphasizing its operation under pressure, the use of pumping stations, and the role of water towers in maintaining both efficiency and robustness, especially during peak demand and power failures.

15:07

🏙️ The Aesthetics and Functionality of Water Towers

The paragraph celebrates the water tower as a piece of civil infrastructure, discussing its various architectural styles and its importance in providing a continuous water supply. It argues against the notion that water towers are unsightly, instead viewing them as icons of engineering and community history. The paragraph also explains the practical aspects of water towers, such as their capacity to supply water during emergencies and their role in the water distribution system.

20:09

🚰 Design and Challenges of Water Distribution Networks

The paragraph delves into the design of water distribution networks, including the use of interconnected loops and grids to prevent service disruptions during maintenance. It discusses the challenges of maintaining pressure in water mains and the need for shut-off valves for isolation during repairs. The text also addresses the specific considerations for water pressure in high-rise buildings and the private component of the water system, including service lines, curb valves, water meters, and interior shut-off valves.

25:10

🔄 Water Hammer and the Private Water System Infrastructure

The final paragraph discusses the private aspect of the water system, including the service line from the main to individual homes, the curb valve, water meter, and interior shut-off valve. It explains the concept of water hammer, a pressure shock that can occur when water flow is suddenly stopped, and how it is mitigated using air-filled expansion chambers. The paragraph concludes by reflecting on the entire water system, from its collection as runoff to its delivery to homes, emphasizing the engineering marvel of this everyday technology.

Keywords

💡Raw Water

Raw water refers to water that is collected from natural sources such as rivers, lakes, or wells and is yet to be treated for human consumption. In the video's context, raw water is the starting point for the water supply process, which still contains various contaminants and is not safe to drink without further treatment. The script mentions that regardless of the source, raw water requires purification processes to make it suitable for its many uses, including drinking and industrial applications.

💡Contaminants

Contaminants are impurities or substances that can cause harm or discomfort when present in water. The script discusses various types of contaminants found in raw water, such as microorganisms, dissolved salts and metals, inorganic chemicals like arsenic and lead, and organic compounds. These contaminants can be naturally occurring or result from human activities and pose a risk to human health, which is why they must be removed or neutralized during water treatment.

💡Water Treatment

Water treatment is the process of purifying raw water to make it safe for human consumption. The video script describes the various stages of water treatment, including clarification, filtration, and disinfection. This process is essential to remove contaminants and ensure that the water supply is free from harmful substances, thereby protecting public health.

💡Environmental Protection Agency (EPA)

The EPA is a U.S. government agency responsible for enforcing regulations to protect human health and the environment. In the context of the video, the EPA sets and enforces maximum permissible levels for over 80 contaminants in drinking water, ensuring that public water systems comply with the Safe Drinking Water Act of 1974. The EPA's role is crucial in maintaining water quality and safety standards.

💡Clarification

Clarification is the first step in the water treatment process, aimed at removing suspended particles and impurities from the water. The script illustrates this process using a chemical coagulant, such as Alum, which neutralizes the charges of suspended particles, causing them to clump together and settle at the bottom of the treatment basin. This process is vital for improving water quality before further treatment stages.

💡Filtration

Filtration is the process of physically removing particulate matter from water by passing it through a medium that traps the particles. The script describes a typical filtration system composed of layers of gravel, sand, and anthracite coal. Filtration is essential for capturing any remaining impurities that were not removed during clarification, thus further purifying the water.

💡Disinfection

Disinfection is the final step in the water treatment process, where chemical or physical methods are used to kill or inactivate microorganisms in the water. The script mentions the use of dissolved chlorine, ultraviolet light, or ozone as disinfectants. This step ensures that the water is free from harmful bacteria and viruses before it is distributed for consumption.

💡Desalination

Desalination is the process of removing salt and other minerals from seawater to produce fresh water suitable for drinking and irrigation. The script discusses the importance of desalination, especially in areas where freshwater is scarce. The process, which often involves reverse osmosis, is energy-intensive but is becoming more viable due to technological advances and the need for alternative water sources.

💡Water Distribution System

A water distribution system is a network of pipes and infrastructure that delivers treated water from the treatment plant to consumers. The script explains that this system operates under pressure and includes water mains, service lines, valves, and water towers. The system's design and operation are critical to ensuring a continuous supply of water at the right pressure to meet consumer demand.

💡Water Tower

A water tower is a tall structure that stores water and provides additional pressure to the water distribution system. The script highlights the importance of water towers in maintaining water pressure, especially during peak demand periods, and as a backup during power outages. Water towers also play a role in the aesthetic and cultural identity of communities.

💡Water Main

A water main is a large pipe that carries water from the treatment plant to the distribution network. The script describes water mains as typically being made of iron, located underground, and arranged in interconnected loops or grids to ensure efficient water supply and ease of maintenance. The design of water mains is crucial for the reliability and resilience of the water distribution system.

Highlights

Raw water from various sources is not ready for human consumption and may contain various contaminants, including microorganisms and heavy metals.

Some contaminants like arsenic, lead, and mercury originate from natural deposits, while others are the result of human activities.

Environmental regulations and engineering solutions can significantly reduce but not completely eliminate water contamination.

The Safe Drinking Water Act of 1974 mandates the EPA to regulate water quality and set standards for public safety.

Environmental engineers play a crucial role in designing water treatment facilities tailored to community needs and water resources.

Water treatment processes include clarification, filtration, and disinfection to ensure water safety.

Algae blooms in reservoirs can be mitigated through storm runoff management or mechanical and chemical treatments.

Desalination, especially through reverse osmosis, is becoming more prevalent due to technological advances, providing fresh water to arid regions.

Water distribution systems operate under pressure, utilizing water towers and pumps to maintain supply and handle demand fluctuations.

Water towers are essential for providing continuous water supply during power outages and for firefighting needs.

Water distribution networks are designed with interconnected loops to ensure redundancy and ease of maintenance.

Pressure regulation in water distribution systems is critical, especially in high-rise buildings requiring specific pump systems.

Service lines and curb valves are part of the private water infrastructure connecting homes to the public water supply.

Water hammer can cause damage in plumbing systems, and expansion chambers are used to mitigate its effects.

The water distribution system is an everyday engineering marvel, delivering water from collection to treatment and finally to consumers.

The water cycle's full picture includes not only distribution but also the wastewater disposal and treatment processes.

Water towers are not just functional; they can also be architectural landmarks and symbols of community pride.

Transcripts

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thus far in our exploration of water

supply we've examined the Technologies

used to collect raw water from a

watershed and then transport it to the

municipality where it will be used not

only for drinking but also for cooking

personal hygiene washing clothes and

dishes circulating heat through homes

watering Lawns a wide array of

commercial and Industrial purposes as

well but regardless of whether it's been

delivered by an aqueduct pumped from a

well or drawn from a nearby lake this is

still raw water and as the name implies

it isn't ready for human consumption

just yet raw water from certain kinds of

sources an Upland spring or a deep

groundwater well for example might be

reasonably pure and potable that is safe

for drinking but most raw water

particularly surface water is loaded

with contaminants some of which can be

extremely hazardous to human health

these contaminants include

microorganisms such as viruses BAC Bia

and protozoa dissolved salts and metals

like sodium calcium and magnesium other

inorganic chemicals like arsenic

asbestos cadmium lead Mercury nitrates

organic chemical compounds like Benzene

dioxin and polychlorinated bif phenols

or pcbs and even radioactive uranium and

radium some of this contamination is

beyond human control for example one of

those nasty microorganisms the

Legionella bacteria which causes

legionaire disease is found naturally in

the environment arsenic lead Mercury and

radioactive particles can originate from

the erosion of natural deposits calcium

and magnesium are dissolved into

groundwater when it percolates through

geologic formations of limestone chalk

or Dolomite by the way this process is

the cause of so-called hard

water but most contain contamination of

raw water is caused by human activity in

the Watershed dangerous pathogens like

cryptosporidium and Giardia originate

from human and animal feces many

chemical contaminants are discharged

from industrial facilities petroleum

refineries steel mills chemical plants

pulp Mills and mines cadmium enters our

water from the corrosion of galvanized

steel pipes and improper disposal of

batteries and paints nitrates come

primarily from f fertilizers carried

from agricultural land and residential

yards by storm runoff much organic

chemical contamination originates from

the use of herbicides and insecticides

again transported into our water supply

by storm

runoff clearly then water quality can be

improved to some extent by controlling

the human causes of

contamination by designing effective

sewage treatment and storm Water

Management Systems constructing land

landfills with proper containment

minimizing industrial pollution using

agricultural methods that control

erosion and reduce excess application of

fertilizers and pesticides refraining

from using these chemicals in our own

yards and promoting the responsible

handling and disposal of fuel motor oil

batteries and other hazardous

materials when implemented

comprehensively and conscientiously

these sorts of measures can

significantly reduce the contamination

of our Raw water sources but they can't

eliminate it Agricultural and

Manufacturing are integral to our

prosperity and quality of life many of

these industries unhealthy byproducts

are essentially Inseparable from the

benefits that we enjoy and are very

difficult to dispose of in an effective

environmentally responsible

manner thus some level of contamination

is practically inevitable and Municipal

Water Supply systems always require some

level of treatment in the US under the

provisions of the Safe Drinking Water

Act of

1974 the Environmental Protection Agency

has primary responsibility for

regulating water quality to ensure

Public Safety the EPA fulfills this

responsibility by setting and enforcing

maximum permissible levels for over 80

possible

contaminants EPA rules also specify in

general terms the treatment processes

required of all Public Water Systems

though individual municipalities do have

the flexibility to adapt these processes

to their own

needs this is the business of

environmental Engineers the unsung

heroes who design build and operate

water treatment facilities and processes

consistent with the given community's

needs and available Water Resources in

this endeavor the engineers are greatly

aided by environmental scientists and

chemists who develop the protocols and

Technologies for testing water to

determine contamination concentrations

accurately so let's talk about water

treatment and while our primary focus

will be on your local Water Treatment

Plant it's important to recognize that

some aspects of water purification begin

before the raw water ever reaches this

facility when water is impounded in a

reservoir or lake a number of water

quality problems may result the first is

the growth of algae and aquatic plants

which feed on ferti fertilizers that are

washed into the reservoir by storm

runoff this satellite photo shows a huge

algae bloom in Lake Erie and its

proximity to the Shoreline suggests an

intimate connection to runoff from the

lake shore some algae and plants are

toxic but most are just a nuisance they

give the water an unpleasant taste and

may follow pipelines and

pumps the best defense against algae is

to deny it food by using storm runoff

management to keep fertilizers out of

the reservoir if this approach isn't

feasible then the algae can be removed

mechanically using a device like this

algy Harvester or they can be killed by

treating the water with a chemical

copper

sulfate but this chemical must be used

with some caution not only can copper

sulfate be toxic to fish if it's used in

excessively high concentrations can also

exacerbate another problem that's often

encountered in Reservoir management that

problem is called an oxia the depletion

of dissolved oxygen near the bottom of a

body of

water anoxia can occur naturally as a

result of inadequate water circulation

but if copper sulfate treatments kill

too much algae too fast the loss of

dissolved oxygen will be greatly

accelerated by the oxidation of all this

rotting organic material an oxia kills

fish they actually suffocate for lack of

oxygen and it also encourages the growth

grow of anerobic bacteria which give the

water a foul smell the cure for anoxia

is Iration which restores oxygen to the

water now a century ago this process was

accomplished by installing elaborate

fountains near the outlet works of a

reservoir just like this one at the

Ashokan Reservoir today however

environmental Engineers use a technique

that's less splashy but more effective

an air compressor on Shore forces air

through a pipe to a fixture located at

the bottom of the reservoir this device

works just like the airator in a home

aquarium sending a continuous stream of

bubbles up to the surface these bubbles

add oxygen to the water in the immediate

vicinity of the air raater but more

importantly the upward stream sets up a

circulation pattern that effectively

turns the lake upside down drawing the

oxygen starved water up to the surface

where it can be replenished naturally

now onward to the water treatment plant

which uses an integrated series of

mechanical and chemical processes to

perform three basic functions

clarification filtration and

disinfection let's use this process

diagram to explore step by step how

these functions are

performed as raw water is pumped from a

lake river or receiving Reservoir into

the treatment plant it passes through a

series of progressively finer gradings

and screens to remove trash leaves

aquatic weed s and critters like fish

tadpoles and zebra muscles which have no

business swimming around in our drinking

water the water then enters a mixing

Basin where a chemical coagulant is

added and vigorously mixed the purpose

of the coagulant is to neutralize the

electrical charges that cause suspended

particles in the water to repel each

other the coagulant causes these

particles to cling together forming

progressively larger clumps of

impurities called flocks this process

called floculation concludes when the

flocks get so heavy that they settle

down to the bottom of the Basin now

let's see how this clarification process

works here's a container of some very

dirty water that I obtain from a local

swamp I guarantee you no water this

dirty is ever going to be admitted into

a water treatment facility but I've used

it here really just to exaggerate the

effect of that chemical coagulant that

I'm about to demonstrate I'm going to

mix into this

water a substance called Alum a common

chemical coagulant that's often used for

cleaning swimming pools I'll add the

Alum I'll mix it

vigorously to dissolve those crystals

into the

water see how it

works now in the treatment plant this

mixture of raw water and coagulant now

passes from the mixing Basin into a

floculation chamber where the coagulant

does its magic here the water is gently

mixed so the fine particles will

continue to encounter each other but

without breaking up the ever growing

flocks with floculation underway the

stream passes into a sedimentation Basin

where the water is stilled and the

flocks sink to the

bottom this accumulated sludge is

periodically Rak out dried and disposed

of in a landfill now it generally takes

30 minutes to an hour for the

floculation and sedimentation processes

to play out so we won't really start to

see significant results in this

experiment until the end of the

lecture but about 45 minutes ago I added

the same amount of Alum to a sample of

equally dirty water and here it is

now it certainly isn't perfectly clean

but I think you can see why this first

phase of water treatment is called

clarification back at the treatment

plant the clarified water is now pumped

through a filter typically composed of

horizontal layers of gravel sand and

anthracite coal as the water passes

through this filter any particulate

matter that didn't settle out during

clarification is captured in the tiny

voids between the sand grains the coal

serves as a source of carbon which is

particularly effective at capturing

volatile organic chemicals and removing

them from the

water with filtration complete the water

is disinfected usually by mixing in a

small quantity of dissolved chlorine

which kills any bacteria or viruses that

might have survived clarification and

filtration alternative methods of

disinfection include exposing the water

to ultraviolet light or ozone both of

these methods are also quite effective

at killing

pathogens finally the purified water

passes into a holding tank which gives

the chlorine more time for disinfection

while also providing a reservoir for

smoothing out fluctuations in demand at

this point the water treatment process

is complete and the finished water

enters the local distribution system but

before we examine water distribution I

need to say a few words about a

different type of water treatment

process a process that converts seawater

into drinking water for roughly 300

million people around the globe this

process called desalination has been

around for a long time but it's

undergoing a major surge in popularity

today as a result of recent

technological

advances the most important of these is

a technology called reverse osmosis

which removes salt from seawater by

forcing it through a membrane Under

Pressure these sorts of improved

technologies have cut the cost of

desalination in half over the past

decade nonetheless desalination is still

significantly more energy intensive

therefore more expensive than treating

surface water or groundwater and its

economic viability is further

constrained by the fact that seawater is

always obtained at a low elevation a Sea

Coast and thus must always be pumped to

a higher elevation and transported

Inland for

consumption nonetheless there are places

in the world like Oman shown here where

desalinated seawater is practically the

only reliable water Source available to

entire

populations another such place is Israel

where the recent construction of several

high capacity desalination plants have

provided this drought-ridden country

with the capacity to produce Surplus

drinking water for the first time in its

history as the technology continues to

improve we can expect to see more of

this trend for example the cities of Los

Angeles and San Diego are currently

considering the construction of

desalination plants as a means of

addressing their persistent water supply

challenges now back to our local water

distribution system a single most

important characteristic of this system

a characteristic that distinguishes it

from both storm drainage and sanitary

sewer systems is that water distribution

operates under pressure to use the

Hydraulics terminology I introduced in

the last lecture water distribution is

based on pipe flow rather than open

Channel flow principle

the pressure that makes a pipe flow

system work can be provided by gravity

but only in the rare circumstance where

the water treatment facility is located

at a higher elevation than every

consumer served by the distribution

system in all other cases the pressure

must be supplied by one or more pumping

stations often housed in a non-descript

building like this one and using one or

more electric pumps to Propel water from

the treatment plant into the

distribution Network

the network is composed of large pipes

called water mains smaller pipes called

service lines connectors valves fire

hydrants and most importantly an

intermediate storage facility which

greatly enhances both the efficiency and

robustness of this system let's see how

this ingenious system

works this container of water represents

the finished water holding tank at a

water treatment facility I'm going to

use this electric pump to represent the

pumping station and as you can see I'm

using plastic tubing to represent the

water main and the service lines

branching out from the water mains to

individual residences and here is our

intermediate storage facility typically

a Water Tower located on High Ground

close to the population it serves now

let's say that it's midnight most of the

town is a sleep so there's very little

demand for water nonetheless the pump is

running and because all of these faucets

and shower heads are closed most of the

water is being pupped up into the water

tower through this Central conduit at

the base of the

Tower by the time morning arrives the

tank is quite full and that's good

because within a 2 or three hour period

practically everyone in town will open a

faucet take a shower shave or make a pot

of

coffee resulting in significant

additional demand for water the pump now

can't keep up with a sudden surge in

demand that's okay because as the

pressure in the water M drops water

automatically begins flowing back into

the pipe Network in effect the water

tower is now providing additional

pressure to help the pump meet Peak

demand now later in the morning people

head off to work and the demand drops

off

considerably perhaps even enough for the

water tower to begin refilling but only

till dinner time when demand Peaks again

and the water tower once again

supplements the pump finally nightfalls

and the cycle begins

again now two aspects of this ingenious

system are worth

emphasizing first it's highly efficient

because without that water tower a much

larger pump or perhaps several larger

pumps would be required to meet the peak

demand second the system is robust

because the tower will continue to

supply water even if a power failure

shuts down the electric pumps I should

add that most Municipal Water Systems

are required by law to have backup Power

Systems typically diesel or gas

generators for their pumping stations

but backup generators won't necessarily

kick in instantaneously after a power

outage so the water tower is critical

for providing continuity of

Supply this is particularly important

because water Distribution Systems

Supply fire hydrants as well as

residences and businesses and the

emergency that knocks out electrical

power might be a fire that's why an

intermediate storage facility is usually

designed to have enough capacity to

supply the municipality for at least one

full day plus the additional water

required to fight a

fire

you know I have occasionally heard it

said that water towers are ugly that

they're an obtrusive utilitarian blight

on our landscape I beg to differ the

water tower is a beautiful icon of our

civil infrastructure a simple robust

technology that clearly manifests the

laws of physics underlying its design

that makes life incalculably better for

the many thousands of people living in

its shadow that that almost always tells

us something about the era and the

community in which it was

built the water tower can be a humble

piece of Americana or the symbol of a

great City it can be futuristic or

traditional High style or brutally

simple it can be Whimsical or serious

architecturally distinctive or even

Majestic the water tower can be an

expression of civic pride and

patriotism a vocative of history and

culture sometimes demanding to be seen

sometimes preferring to remain hidden

often doing double duty as a high perch

for cellular phone antennas occasionally

just bidding us to have a nice day you

know if I accomplish nothing else in

this course I hope I can convince you

that the humble water tower is a piece

of everyday technology that's worth

noticing and worth celebrating

now back to the water distribution

Network which is somewhat less colorful

than the water tower but no less

important water Ms are large pipes

generally at least 6 Ines in diameter

but often much larger sometimes made of

PVC plastic or steel but most often made

of iron which resists corrosion better

than steel and corrosion is the most

common cause of those water main breaks

you're always hearing about on the

Evening News these pipes are almost

always located underground to protect

them against freezing as such the depth

varies from 3 to 4 ft in the southern us

to 6 to 8 feet in the northern states to

12 to 15 feet in

Alaska as this computer model

illustrates water mains generally follow

public streets because the municipality

already owns the RightWay here storm

drains and sanitary sewers also follow

the public streets and because all three

of these systems have distinct different

points of origin and distinctly

different destinations there's a great

potential for them to interfere with

each other when such conflicts occur

it's always the water man that dips

beneath or bends around the other two

systems can you guess

why hopefully you recall that storm

drains and sanitary sewers operate under

the principle of open Channel flow and

so their channels must be constructed on

a steady downhill gradient without

exception conversely the water

distribution system is the only one of

the three that operates under pressure

thus water mains can change gradient and

Direction with no problem even flowing

uphill when necessary to avoid a

conflict with a storm drain or sewer for

this same reason water Ms typically

don't use the river-like topology we saw

in storm drainage systems with many

small tributaries flowing into

progressively smaller numbers of larger

streams ideally water s are arranged in

interconnected Loops which can also be

visualized as a grid

pattern deadend Branch lines are used

only where Loops are impossible for

example at culde

acts so why are Loops better than

branches well suppose the water main

failed at this location it would be easy

to isolate this small section of the

main and make the necessary repairs

disrupting water supply to only a very

limited number of homes thank to this

looped

configuration water can flow through a

main in either direction and because the

system is pressurized the water will

always find its own path around a closed

segment like this of course to fully

realize this Advantage the distribution

Network must have lots of shut off

valves that can be used to isolate any

segment of the system for maintenance

and repair and as this diagram indicates

modern water systems do include lots of

valves when you see one of these metal

covers at street level there's usually a

shut off valve a few feet

below on the other hand with a branched

topology a failure here would cause many

more homes to lose their water supply

until the repair was completed this

situation is sufficiently problematic

that in many municipalities the

developer is required to provide an

easement allowing the utility company to

run a water main across private property

to the next culdesac turning two

branches into a loop like this

now the greatest challenge in designing

a water distribution network is

maintaining an appropriate level of

pressure throughout the system most

systems operate with water mains

pressurized between 40 and 60 pounds per

square inch or PSI as a point of

comparison the pressure in your car

tires is about 30 PSI at pressures above

80 psi Residential Plumbing fixtures and

pipe joints will start leaking and below

20 psi the flow of water to a third

story shower head will be little more

than a dribble if the region served by

the water distribution system has large

changes in elevation the system must

typically be divided into several

pressure zones interconnected with

special pressure regulating

valves perhaps the greatest challenge in

regulating water pressure is in a

high-rise building where heavyduty pumps

are required to move the water from

ground level up to the highest floors in

general one PSI of pressure will lift

water 2.3 ft thus One World Trade Center

would require over 500 PSI at ground

level to move water all the way up to

its highest occupied floor at 1268 ft of

course this would cause the pressure at

ground level to be impractically high

thus most tall buildings use a series of

pumps placed at regular intervals from

bottom to top and even then pressure

relief valves must be used for the water

distribution lines in the immediate

vicinity of the

pumps now thus far we've been looking at

the public component of the water

distribution system the water treatment

plant intermediate storage facility and

water mains but there's a private

component too and it begins underneath a

street in front of your home where a

copper or plastic service line branches

off from the main and conveys a stream

of potable water into your plumbing

system at your property line is a curb

valve which can be used to cut off your

entire water supply from outside your

home either for maintenance or if you

don't pay your water bill beyond the

curb valve the service line enters your

home through a hole in the foundation

wall or floor slab just inside is your

water meter and an interior shut off

valve this is the one you want to close

to keep your basement from flooding when

a pipe

bursts from here a separate pipe

branches off of the main surface line to

supply the hot water heater from this

point forward the hot and cold water

lines run parallel to each other

throughout the building supplying sinks

tubs and showers while the cold water

line also individually supplies toilets

exterior spigots and perhaps an ice

maker in your

refrigerator throughout this network

whenever you open a faucet turn on a

shower use a washing machine or flush a

toilet water flows freely because of the

combined effects of a distant pumping

station

and a water tower which Supply the

pressure that makes the system

work but pressure is a double-edged

sword water that's flowing through a

pipe under pressure has considerable

momentum if the flow is shut off

Suddenly by quickly closing a faucet for

example the resulting shock called water

hammer can damage pipe joints and

fixtures to prevent water hammer water

supply lines are fitted with these airf

filled expansion Chambers which affect

absorb the

shock well you open a faucet and clear

clean water flows let's close today's

lecture by reflecting on where that

stream of water originated as surface

runoff in a distant Watershed impounded

as raw water in a reservoir created by a

dam collected and transported through an

aqueduct to a water treatment

plant clarified filtered and disinfected

through an integrated series of physical

and chemical processes and then

delivered to your kitchen sink at just

the right pressure by a robust redundant

network of pumps pipes Valves and water

towers this is the epitome of everyday

engineering an immense integrated

multi-dimensional technological system

which we're largely

unaware delivering this precious life

sustaining substance on demand

but in a broader sense we've only really

seen half of this system our water

distribution system supplies 150 gallons

per person per day what happens to all

this stuff after we've used it next

we'll answer this question as we explore

the most aromatic aspect of everyday

engineering Wastewater disposal and

treatment