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