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Our grandparents' generation
created an amazing system
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of canals and reservoirs
that made it possible
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for people to live in places
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
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and Los Angeles to provide water
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for people who lived
in a really dry place.
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In the 20th century,
we literally spent trillions of dollars
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building infrastructure
to get water to our cities.
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In terms of economic development,
it was a great investment.
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But in the last decade,
we've seen the combined effects
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of climate change, population growth
and competition for water resources
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threaten these vital lifelines
and water resources.
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This figure shows you the change
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.
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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
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that they referred to as the "Third Straw"
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to pull water water
out of the greater depths of the lake.
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The challenges associated
with providing water to a modern city
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are not restricted
to the American Southwest.
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In the year 2007, the third largest
city in Australia, Brisbane,
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came within 6 months
of running out of water.
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A similar drama is playing out today
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,
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to being nearly empty today
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as the city approaches
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,
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we've never truly experienced
the effects of a catastrophic drought.
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We like to complain
about the navy showers we have to take.
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We like our neighbors to see
our dirty cars and our brown lawns.
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But we've never really faced
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,
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it's always been possible
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,
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it's not going to be possible
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
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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.
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And even if we succeed in grabbing
the water from our rural neighbors,
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we're just transferring
the problem to someone else
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and there's a good chance
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.
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I think that there's a better way
to solve our urban water crisis
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and I think that's to open up
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
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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
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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,
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I probably would have dismissed you
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
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have shown me that we have
the technologies and the management skills
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to actually transition away
from imported water,
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and that's what I want
to tell you about tonight.
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The first source of local water
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.
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One of the great tragedies
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.
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And when we did that,
we had to build storm sewers
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to get the water
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.
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Let me give you an example.
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This figure here shows you
the volume of water
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that could be collected
in the city of San Jose
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if they could harvest the stormwater
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
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that if San Jose could just capture half
of the water that fell within the city,
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they'd have enough water
to get them through an entire year.
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Now, I know what some of you
are probably thinking.
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"The answer to our problem
is to start building great big tanks
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and attaching them
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.
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But if you live in a place
where it mainly rains in the winter time
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and most of the water demand
is in the summertime,
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it's not a very cost-effective way
to solve a water problem.
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And if you experience the effects
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.
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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,
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and that's to capture it
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
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that can accommodate
huge volumes of water.
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For example, historically,
Los Angeles has obtained
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about a third of its water supply
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
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and runs off of your lawn
and flows down the gutter,
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you might say to yourself,
"Do I really want to drink that stuff?"
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Well, the answer is
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
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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
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with a new project that they're building
in Burbank, California.
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This figure here shows
the stormwater park that they're building
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by hooking a series of stormwater
collection systems, or storm sewers,
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and routing that water
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,
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and then it goes
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.
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And in the process
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
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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
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after it's been through
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
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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
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will flow with the wastewater
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that comes out
of our sewage treatment plants.
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Now, many of you are probably familiar
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
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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.
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We've been doing this
for a couple of decades now.
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But what we're learning
from our experience
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is that this approach is much more
expensive that we expected it to be.
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Because once we build
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
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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.
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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
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is to turn treated wastewater
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
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and pass it through
a reverse osmosis membrane:
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a thin, permeable plastic membrane
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that allows water molecules
to pass through
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but traps and retains the salts,
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
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into two parts that are called
hydroxyl radicals,
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and these hydroxyl radicals
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,
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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
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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,
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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
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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
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on the Santa Ana River
in Southern California.
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The treatment wetland receives water
from a part of the Santa Ana River
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that in the summertime consists
almost entirely of wastewater effluent
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from cities like Riverside
and San Bernardino.
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The water comes
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,
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remove the nutrients
and inactivate the waterborne pathogens.
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The water gets put back
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,
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and becomes the drinking water
of the city of Anaheim,
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completing the trip
from the sewers of Riverside County
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to the drinking water supply
of Orange County.
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Now, you might think
that this idea of drinking wastewater
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is some sort of futuristic fantasy
or not commonly done.
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Well, in California, we already recycle
about 40 billion gallons a year
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of wastewater through the two-stage
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
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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,
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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.
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And the place where we need to think
about water conservation is outdoors
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because in California
and other modern American cities,
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about half of our water use
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
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with about half as much water.
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So there's no need
to start painting concrete green
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and putting in Astroturf
and buying cactuses.
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We can have California-friendly
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.
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The fourth and final water tap
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.
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"It's a great thing to do if you have
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.
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But that characterization
of seawater desalination
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as being a nonstarter
is hopelessly out of date.
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We've made tremendous progress
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
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that's currently being built
north of San Diego.
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Compared to the seawater
desalination plant
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that was built in
Santa Barbara 25 years ago,
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this treatment plant
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,
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doesn't mean we should start building
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.
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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.
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Through reform in the way we landscape
our surfaces and our properties,
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we can reduce outdoor water use
by about 50 percent,
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thereby increasing
the water supply by 25 percent.
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We can recycle the water
that makes it into the sewer,
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thereby increasing
our water supply by 40 percent.
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And we can make up the difference
through a combination
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of stormwater harvesting
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
-
that climate change throws at us
in the coming years.
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Let's create a water supply
that uses local sources
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and leaves more water
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.
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And let's do it for our children
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
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because it's our last chance
to create a new kind of water system.
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Thank you very much for your attention.
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(Applause)