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.