13:38
TEDxMarin

David Sedlak: 4 ways we can avoid a catastrophic drought

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As the world's climate patterns continue to shift unpredictably, places where drinking water was once abundant may soon find reservoirs dry and groundwater aquifers depleted. In this talk, civil and environmental engineer David Sedlak shares four practical solutions to the ongoing urban water crisis. His goal: to shift our water supply towards new, local sources of water and create a system that is capable of withstanding any of the challenges climate change may throw at us in the coming years.

- Civil and environmental engineer
David Sedlak’s research focuses the long-term goal of developing cost-effective, safe and sustainable systems to manage water resources. Full bio

Our grandparents' generation
created an amazing system
00:12
of canals and reservoirs
that made it possible
00:16
for people to live in places
where there wasn't a lot of water.
00:19
For example, during the Great Depression,
00:22
they created the Hoover Dam,
00:25
which in turn, created Lake Mead
00:26
and made it possible for the cities
of Las Vegas and Phoenix
00:29
and Los Angeles to provide water
00:32
for people who lived
in a really dry place.
00:34
In the 20th century,
we literally spent trillions of dollars
00:37
building infrastructure
to get water to our cities.
00:41
In terms of economic development,
it was a great investment.
00:45
But in the last decade,
we've seen the combined effects
00:49
of climate change, population growth
and competition for water resources
00:52
threaten these vital lifelines
and water resources.
00:57
This figure shows you the change
in the lake level of Lake Mead
01:01
that happened in the last 15 years.
01:05
You can see starting around the year 2000,
01:07
the lake level started to drop.
01:10
And it was dropping at such a rate
01:12
that it would have left the drinking water
intakes for Las Vegas high and dry.
01:14
The city became so concerned about this
01:18
that they recently constructed
a new drinking water intake structure
01:21
that they referred to as the "Third Straw"
01:25
to pull water out
of the greater depths of the lake.
01:27
The challenges associated
with providing water to a modern city
01:31
are not restricted
to the American Southwest.
01:34
In the year 2007, the third largest
city in Australia, Brisbane,
01:37
came within 6 months
of running out of water.
01:43
A similar drama is playing out today
in São Paulo, Brazil,
01:46
where the main reservoir for the city
01:50
has gone from being
completely full in 2010,
01:52
to being nearly empty today
01:55
as the city approaches
the 2016 Summer Olympics.
01:57
For those of us who are fortunate enough
02:01
to live in one
of the world's great cities,
02:04
we've never truly experienced
the effects of a catastrophic drought.
02:06
We like to complain
about the navy showers we have to take.
02:10
We like our neighbors to see
our dirty cars and our brown lawns.
02:14
But we've never really faced
the prospect of turning on the tap
02:18
and having nothing come out.
02:22
And that's because when things
have gotten bad in the past,
02:24
it's always been possible
to expand a reservoir
02:27
or dig a few more groundwater wells.
02:30
Well, in a time when all
of the water resources are spoken for,
02:34
it's not going to be possible
to rely on this tried and true way
02:37
of providing ourselves with water.
02:41
Some people think that we're going
to solve the urban water problem
02:43
by taking water from our rural neighbors.
02:47
But that's an approach that's fraught
with political, legal and social dangers.
02:50
And even if we succeed in grabbing
the water from our rural neighbors,
02:56
we're just transferring
the problem to someone else
03:00
and there's a good chance
it will come back and bite us
03:02
in the form of higher food prices
03:05
and damage to the aquatic ecosystems
that already rely upon that water.
03:07
I think that there's a better way
to solve our urban water crisis
03:12
and I think that's to open up
four new local sources of water
03:15
that I liken to faucets.
03:19
If we can make smart investments
in these new sources of water
03:21
in the coming years,
03:25
we can solve our urban water problem
03:27
and decrease the likelihood
that we'll ever run across
03:29
the effects of a catastrophic drought.
03:32
Now, if you told me 20 years ago
03:36
that a modern city could exist
without a supply of imported water,
03:38
I probably would have dismissed you
as an unrealistic and uninformed dreamer.
03:42
But my own experiences
03:47
working with some of the world's most
water-starved cities in the last decades
03:48
have shown me that we have
the technologies and the management skills
03:53
to actually transition away
from imported water,
03:57
and that's what I want
to tell you about tonight.
04:00
The first source of local water
supply that we need to develop
04:03
to solve our urban water problem
04:07
will flow with the rainwater
that falls in our cities.
04:09
One of the great tragedies
of urban development
04:13
is that as our cities grew,
04:16
we started covering all the surfaces
with concrete and asphalt.
04:18
And when we did that,
we had to build storm sewers
04:22
to get the water
that fell on the cities out
04:24
before it could cause flooding,
04:26
and that's a waste
of a vital water resource.
04:28
Let me give you an example.
04:32
This figure here shows you
the volume of water
04:33
that could be collected
in the city of San Jose
04:37
if they could harvest the stormwater
that fell within the city limits.
04:39
You can see from the intersection
of the blue line and the black dotted line
04:43
that if San Jose could just capture half
of the water that fell within the city,
04:48
they'd have enough water
to get them through an entire year.
04:52
Now, I know what some of you
are probably thinking.
04:56
"The answer to our problem
is to start building great big tanks
04:58
and attaching them
to the downspouts of our roof gutters,
05:02
rainwater harvesting."
05:05
Now, that's an idea
that might work in some places.
05:07
But if you live in a place
where it mainly rains in the winter time
05:09
and most of the water demand
is in the summertime,
05:12
it's not a very cost-effective way
to solve a water problem.
05:15
And if you experience the effects
of a multiyear drought,
05:19
like California's currently experiencing,
05:22
you just can't build a rainwater tank
that's big enough to solve your problem.
05:24
I think there's a lot more practical way
05:28
to harvest the stormwater and
the rainwater that falls in our cities,
05:30
and that's to capture it
and let it percolate into the ground.
05:34
After all, many of our cities are sitting
on top of a natural water storage system
05:37
that can accommodate
huge volumes of water.
05:43
For example, historically,
Los Angeles has obtained
05:46
about a third of its water supply
from a massive aquifer
05:49
that underlies the San Fernando Valley.
05:52
Now, when you look at the water
that comes off of your roof
05:56
and runs off of your lawn
and flows down the gutter,
05:59
you might say to yourself,
"Do I really want to drink that stuff?"
06:01
Well, the answer is
you don't want to drink it
06:05
until it's been treated a little bit.
06:07
And so the challenge that we face
in urban water harvesting
06:09
is to capture the water, clean the water
06:12
and get it underground.
06:15
And that's exactly
what the city of Los Angeles is doing
06:17
with a new project that they're building
in Burbank, California.
06:20
This figure here shows
the stormwater park that they're building
06:24
by hooking a series of stormwater
collection systems, or storm sewers,
06:28
and routing that water
into an abandoned gravel quarry.
06:33
The water that's captured in the quarry
06:37
is slowly passed
through a man-made wetland,
06:39
and then it goes
into that ball field there
06:42
and percolates into the ground,
06:44
recharging the drinking water
aquifer of the city.
06:46
And in the process
of passing through the wetland
06:49
and percolating through the ground,
06:52
the water encounters microbes
that live on the surfaces of the plants
06:54
and the surfaces of the soil,
06:58
and that purifies the water.
06:59
And if the water's
still not clean enough to drink
07:02
after it's been through
this natural treatment process,
07:04
the city can treat it again
07:07
when they pump if back out
of the groundwater aquifers
07:08
before they deliver it to people to drink.
07:11
The second tap that we need to open up
to solve our urban water problem
07:14
will flow with the wastewater
07:18
that comes out
of our sewage treatment plants.
07:20
Now, many of you are probably familiar
with the concept of recycled water.
07:23
You've probably seen signs like this
07:26
that tell you that the shrubbery
and the highway median
07:28
and the local golf course
07:31
is being watered with water
07:33
that used to be
in a sewage treatment plant.
07:35
We've been doing this
for a couple of decades now.
07:38
But what we're learning
from our experience
07:41
is that this approach is much more
expensive that we expected it to be.
07:43
Because once we build
the first few water recycling systems
07:47
close to the sewage treatment plant,
07:50
we have to build longer
and longer pipe networks
07:52
to get that water to where it needs to go.
07:54
And that becomes prohibitive
in terms of cost.
07:57
What we're finding is
08:00
that a much more cost-effective
and practical way of recycling wastewater
08:02
is to turn treated wastewater
into drinking water
08:06
through a two-step process.
08:08
In the first step in this process
we pressurize the water
08:11
and pass it through
a reverse osmosis membrane:
08:14
a thin, permeable plastic membrane
08:16
that allows water molecules
to pass through
08:19
but traps and retains the salts,
the viruses and the organic chemicals
08:21
that might be present in the wastewater.
08:26
In the second step in the process,
08:29
we add a small amount of hydrogen peroxide
08:31
and shine ultraviolet light on the water.
08:33
The ultraviolet light
cleaves the hydrogen peroxide
08:36
into two parts that are called
hydroxyl radicals,
08:39
and these hydroxyl radicals
are very potent forms of oxygen
08:42
that break down most organic chemicals.
08:46
After the water's been
through this two-stage process,
08:50
it's safe to drink.
08:53
I know,
08:54
I've been studying recycled water
08:56
using every measurement technique
known to modern science
08:58
for the past 15 years.
09:02
We've detected some chemicals
09:04
that can make it through
the first step in the process,
09:05
but by the time we get to the second step,
09:08
the advanced oxidation process,
09:10
we rarely see any chemicals present.
09:12
And that's in stark contrast
to the taken-for-granted water supplies
09:14
that we regularly drink all the time.
09:18
There's another way we can recycle water.
09:21
This is an engineered treatment wetland
that we recently built
09:24
on the Santa Ana River
in Southern California.
09:27
The treatment wetland receives water
from a part of the Santa Ana River
09:30
that in the summertime consists
almost entirely of wastewater effluent
09:34
from cities like Riverside
and San Bernardino.
09:38
The water comes
into our treatment wetland,
09:41
it's exposed to sunlight and algae
09:43
and those break down
the organic chemicals,
09:45
remove the nutrients
and inactivate the waterborne pathogens.
09:48
The water gets put back
in the Santa Ana River,
09:51
it flows down to Anaheim,
09:54
gets taken out at Anaheim
and percolated into the ground,
09:56
and becomes the drinking water
of the city of Anaheim,
09:59
completing the trip
from the sewers of Riverside County
10:01
to the drinking water supply
of Orange County.
10:05
Now, you might think
that this idea of drinking wastewater
10:09
is some sort of futuristic fantasy
or not commonly done.
10:13
Well, in California, we already recycle
about 40 billion gallons a year
10:16
of wastewater through the two-stage
advanced treatment process
10:21
I was telling you about.
10:24
That's enough water to be
the supply of about a million people
10:25
if it were their sole water supply.
10:29
The third tap that we need to open up
will not be a tap at all,
10:32
it will be a kind of virtual tap,
10:36
it will be the water conservation
that we manage to do.
10:38
And the place where we need to think
about water conservation is outdoors
10:41
because in California
and other modern American cities,
10:44
about half of our water use
happens outdoors.
10:48
In the current drought,
10:51
we've seen that it's possible
10:53
to have our lawns survive
and our plants survive
10:54
with about half as much water.
10:57
So there's no need
to start painting concrete green
10:59
and putting in Astroturf
and buying cactuses.
11:02
We can have California-friendly
landscaping with soil moisture detectors
11:05
and smart irrigation controllers
11:10
and have beautiful
green landscapes in our cities.
11:12
The fourth and final water tap
that we need to open up
11:15
to solve our urban water problem
11:18
will flow with desalinated seawater.
11:20
Now, I know what you probably heard
people say about seawater desalination.
11:23
"It's a great thing to do if you have
lots of oil, not a lot of water
11:27
and you don't care about climate change."
11:31
Seawater desalination is energy-intensive
no matter how you slice it.
11:33
But that characterization
of seawater desalination
11:38
as being a nonstarter
is hopelessly out of date.
11:40
We've made tremendous progress
in seawater desalination
11:43
in the past two decades.
11:46
This picture shows you
11:48
the largest seawater desalination plant
in the Western hemisphere
11:50
that's currently being built
north of San Diego.
11:54
Compared to the seawater
desalination plant
11:57
that was built in
Santa Barbara 25 years ago,
11:59
this treatment plant
will use about half the energy
12:02
to produce a gallon of water.
12:05
But just because seawater desalination
has become less energy-intensive,
12:07
doesn't mean we should start building
desalination plants everywhere.
12:11
Among the different choices we have,
12:14
it's probably the most energy-intensive
12:16
and potentially environmentally damaging
12:18
of the options to create
a local water supply.
12:20
So there it is.
12:24
With these four sources of water,
12:25
we can move away
from our reliance on imported water.
12:27
Through reform in the way we landscape
our surfaces and our properties,
12:31
we can reduce outdoor water use
by about 50 percent,
12:36
thereby increasing
the water supply by 25 percent.
12:39
We can recycle the water
that makes it into the sewer,
12:42
thereby increasing
our water supply by 40 percent.
12:45
And we can make up the difference
through a combination
12:48
of stormwater harvesting
and seawater desalination.
12:51
So, let's create a water supply
12:55
that will be able
to withstand any of the challenges
12:59
that climate change throws at us
in the coming years.
13:02
Let's create a water supply
that uses local sources
13:05
and leaves more water
in the environment for fish and for food.
13:08
Let's create a water system that's
consistent with out environmental values.
13:13
And let's do it for our children
and our grandchildren
13:18
and let's tell them this is the system
13:22
that they have to
take care of in the future
13:24
because it's our last chance
to create a new kind of water system.
13:27
Thank you very much for your attention.
13:31
(Applause)
13:32

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About the Speaker:

David Sedlak - Civil and environmental engineer
David Sedlak’s research focuses the long-term goal of developing cost-effective, safe and sustainable systems to manage water resources.

Why you should listen

Author, Professor and Director of the Institute for Environmental Science and Engineering at UC Berkeley, David Sedlak has developed cost-effective, safe and sustainable systems to manage water resources. He is particularly interested in the development of local sources of water, and his research has addressed water reuse–the practice of using municipal wastewater effluent to sustain aquatic ecosystems and augment drinking water supplies as well as the treatment and use of urban runoff to contaminated groundwater from contaminated industrial sites as water supplies.

In recent years, Sedlak's research on the fate of wastewater-derived contaminants has received considerable attention. He began this research in 1996 when he developed simple methods for measuring steroid hormones in wastewater. Since that time, he and his students have studied the fate of hormones, pharmaceuticals, toxic disinfection byproducts and other chemicals. His research team has also studied approaches for remediating contaminated soil and groundwater by in situ chemical oxidation (ISCO) and advanced oxidation processes.

He also is the author of Water 4.0, a book that examines the ways in which we can gain insight into current water issues by understanding the history of urban water systems.

More profile about the speaker
David Sedlak | Speaker | TED.com