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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
getting water to our cities.
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In terms of economic development,
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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 competitin 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 at 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
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high and dry.
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The city became so concerned about this
that they recently constructed
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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 our 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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is gone from being 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 fortune 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 resevoir
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or dig a few more ground-water 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
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
that 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 draught.
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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 working with
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some of the world's
most water-starved cities
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in the last decades have shown me
that we have the technologies
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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
will flow with the rainwater
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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 our 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 that
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 storm water
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 attach them to the downspouts
of our 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
to harvest the storm water and rain water
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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 storage system
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that can accomdate 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 storm water park
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that they're building by
hooking a series
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of storm water 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
is slowly passed through
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a man made wetland,
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and then it goes into that ballfield then
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 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 it back out
of the groundwater aquifers
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before they deliver it 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 waste water
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that comes out
of our sewer treatment plants.
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Now many of you are probably
familiar with the concept
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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 by water
that used to be
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in a sewage treatment plant.
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We've been going this for
a couple of decades now.
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But what we're learning
from our experience is that
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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 that a much more
cost effective and practical way
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of recycling waste water
is to turn treated waste water
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into drinking water 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 membrane 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 waste water.
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In the second step in the process,
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we had 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 orgenic 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've been studying recycled water
using every measurement technique
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known to modern science
for the past 15 years.
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We've detected some chemicals
that can make it through
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the first step in the process,
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but by the time we make it
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-forgranted 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 California.
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The treatment wetland retrieves water
from the Santa Ana River
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that in the summertime consists
almost entirely of waste water effluent
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from cities like Riverside
and San Bernadino.
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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 inactivates
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,
gets taken out at Anaheim
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and percolated into the ground,
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and becomes the drinking water
for 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
the idea of drinking waste water
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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 waste water 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 modern American cities,
about half of our water usage is outdoors.
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In the current drought,
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we've seen that it's possible to have
out lawns survive
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and our plants survive 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 astroturf and buying cactuses.
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We can have California-friendly
landscaping
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with soil moisture detectors