4 ways we can avoid a catastrophic drought

Our grandparents' generation
created an amazing system

of canals and reservoirs
that made it possible

for people to live in places
where there wasn't a lot of water.

For example, during
The Great Depression,

they created the Hoover Dam,

which in turn, created Lake Mead

and made it possible for the cities
of Las Vegas and Phoenix

and Los Angeles to provide water

for people who lived in
a really dry place.

In the 20th century,
we literally spent trillions of dollars

building infrastructure
getting water to our cities.

In terms of economic development,

it was a great investment.

But in the last decade, we've seen
the combined effects

of climate change, population growth,
and competitin for water resources

threaten these vital lifelines
and water resources.

This figure shows you the change
in the lake level at Lake Mead

that happened in the last 15 years.

You can see starting around
the year 2000,

the lake level started to drop.

And it was dropping at such a rate

that it would have left the drinking
water intakes for Las Vegas

high and dry.

The city became so concerned about this
that they recently constructed

a new drinking water intake structure

that they referred to as the "Third Straw"

to pull water water out of
the greater depths of the lake.

The challenges associated with
providing water to a modern city

are not restricted to
the American Southwest

in the year 2007, the third largest
city in Australia Brisbane

came within 6 months
of running our of water.

A similar drama is playing out today
in São Paulo, Brazil,

where the main reservoir for the city

is gone from being full in 2010,

to being nearly empty today

as the city approaches
the 2016 Summer Olympics.

For those of us who are fortune enough

to live in one of
the world's great cities,

we've never truly experienced the effects
of a catastrophic drought.

We like to complain about
the navy showers we have to take.

We like our neighbors to see
our dirty cars and our brown lawns.

But we've never really faced
the prospect of turning on the tap

and having nothing come out.

And that's because when things
have gotten bad in the past,

it's always been possible to expand
a resevoir

or dig a few more ground-water wells.

Well, in a time when all
of the water resources are spoken for,

it's not going to be possible
to rely on this tried and true way

of providing ourselves with water.

Some people think that we're going
to solve the urban water problem

by taking water from our rural neighbors.

But that's an approach that's fraught
political, legal and social dangers.

And even if we succeed in grabbing
the water from our rural neighbors,

we're just transferring the problem
to someone else

and there's a good chance
that it will come back and bite us,

in the form of higher food prices

and damage to the aquatic ecosystems
that already rely upon that water.

I think that there's a better way
to solve our urban water crisis

and I think that's to open up
four new local sources of water

that I liken to faucets.

If we can make smart investments
in these new sources of water

in the coming years,

we can solve our urban water problem

and decrease the likelihood
that we'll ever run across

the effects of a catastrophic draught.

Now if you told me 20 years ago

that a modern city could exist
without a supply of imported water,

I probably would have dismissed you
as an unrealistic and uninformed dreamer.

But my own experiences working with

some of the world's
most water-starved cities

in the last decades have shown me
that we have the technologies

and the management skills

to actually transition away
from imported water,

and that's what I want to tell
you about tonight.

The first source of local water
supply that we need to develop

to solve our urban water problem
will flow with the rainwater

that falls in our cities.

One of the great tragedies
of urban development

is that as our cities grew,

we started covering all our surfaces
with concrete and asphalt.

And when we did that, we had
to build storm sewers

to get the water that fell
on the cities out

before it could cause flooding,

and that's a waste
of a vital water resource.

Let me give you an example.

This figure here shows you that
the volume of water

that could be collected
in the city of San Jose

if they could harvest the storm water
that fell within the city limits.

You can see from the intersection
of the blue line and the black dotted line

that if San Jose could just capture
half of the water that fell within the city,

they'd have enough water
to get them through an entire year.

Now I know what some of you
are probably thinking,

"The answer to our problem is
to start building great big tanks

and attach them to the downspouts
of our gutters,

rainwater harvesting."

Now, that's an idea that might work
in some places.

But if you live in a place
where it mainly rains in the winter time

and most of the water demand
is in the summertime,

it's not a very cost-effective way
to solve a water problem.

And if you experience the effects
of a multiyear drought,

like California's currently experiencing,

you just can't build a rainwater tank
that's big enough to solve your problem.

I think there's a lot more practical way
to harvest the storm water and rain water

that falls in our cities,

and that's to capture it and let it
percolate into the ground.

After all, many of our cities are sitting
on top of a natural storage system

that can accomdate huge volumes of water.

For example, historically,
Los Angeles has obtained

about a third of its water supply
from a massive aquifer

that underlies the San Fernando valley.

Now when you look at the water
that comes off of your roof

and runs off of your lawn
and flows down the gutter,

you might say to yourself, "Do I really
want to drink that stuff?"

Well, the answer is you don't
want to drink it

until it's been treated a little bit.

And so the challenge that we face
in urban water harvesting

is to capture the water,
clean the water,

and get it underground.

And that's exactly what
the city of Los Angeles is doing

with a new project that they're building
in Burbank, California.

This figure here shows
the storm water park

that they're building by
hooking a series

of storm water collection systems,
or storm sewers,

and routing that water into
an abandoned gravel quarry.

The water that's captured in the quarry
is slowly passed through

a man made wetland,

and then it goes into that ballfield then
and percolates into the ground,

recharging the drinking water aquifer
of the city.

And in the process of passing through
the wetland

and percolating through the ground,

the water encounters microbes
that live on the surfaces of the plants

and the surfaces of the soil,

and that purifies the water.

And if the water's not
clean enough to drink

after it's been through this natural
treatment process,

the city can treat it again

when they pump it back out
of the groundwater aquifers

before they deliver it people to drink.

The second tap that we need to open up
to solve our urban water problem

will flow with the waste water

that comes out
of our sewer treatment plants.

Now many of you are probably
familiar with the concept

of recycled water,

you've probably seen signs like this

that tell you that the shrubbery
and the highway median

and the local golf course

is being watered by water
that used to be

in a sewage treatment plant.

We've been going this for
a couple of decades now.

But what we're learning
from our experience is that

this approach is much more expensive
that we expected it to be.

Because once we build the first few
water recycling systems

close to the sewage treatment plant,

we have to build longer and longer
pipe networks

to get that water to where it needs to go.

And that becomes prohibitive
in terms of cost.

What we're finding is that a much more
cost effective and practical way

of recycling waste water
is to turn treated waste water

into drinking water through
a two-step process.

In the first step in this process
we pressurize the water

and pass it through
a reverse osmosis membrane:

a thin, permeable membrane that allows
water molecules to pass through

but traps and retains the salts,
the viruses and the organic chemicals

that might be present in the waste water.

In the second step in the process,

we had a small amount of hydrogen peroxide

and shine ultraviolet light on the water.

The ultraviolet light cleaves
the hydrogen peroxide

into two parts that are called
Hydroxyl Radicals,

and these Hydroxyl Radicals
are very potent forms of oxygen

that break down most orgenic chemicals.

After the water's been through
this two-stage process,

it's safe to drink.

I've been studying recycled water
using every measurement technique

known to modern science
for the past 15 years.

We've detected some chemicals
that can make it through

the first step in the process,

but by the time we make it
to the second step,

the advanced oxidation process,

we rarely see any chemicals present.

And that's in stark contrast to the
taken-forgranted water supplies

that we regularly drink all the time.