4 ways we can avoid a catastrophic drought | David Sedlak

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 to get 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 competition for water resources

threaten these vital lifelines and water resources.

This figure shows you the change in the lake level of 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 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 out of water.

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

where the main reservoir for the city

has gone from being completely full in 2010,

to being nearly empty today

as the city approaches the 2016 Summer Olympics.

For those of us who are fortunate 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 reservoir

or dig a few more groundwater 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 with 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 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 drought.

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 the 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 the volume of water

that could be collected in the city of San Jose

if they could harvest the stormwater 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 attaching them to the downspouts of our roof 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 stormwater and the rainwater 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 water storage system

that can accommodate 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 stormwater park that they're building

by hooking a series of stormwater 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 ball field there

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 still not clean enough to drink

after it's been through this natural treatment process,

the city can treat it again

when they pump if back out of the groundwater aquifers

before they deliver it to people to drink.

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

will flow with the wastewater

that comes out of our sewage 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 with water

that used to be in a sewage treatment plant.

We've been doing 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 wastewater

is to turn treated wastewater 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 plastic 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 wastewater.

In the second step in the process,

we add 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 organic chemicals.

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

it's safe to drink.

I know,

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 get to the second step,

the advanced oxidation process,

we rarely see any chemicals present.

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

that we regularly drink all the time.

There's another way we can recycle water.

This is an engineered treatment wetland that we recently built

on the Santa Ana River in Southern California.

The treatment wetland receives water from a part of the Santa Ana River

that in the summertime consists almost entirely of wastewater effluent

from cities like Riverside and San Bernardino.

The water comes into our treatment wetland,

it's exposed to sunlight and algae

and those break down the organic chemicals,

remove the nutrients and inactivate the waterborne pathogens.

The water gets put back in the Santa Ana River,

it flows down to Anaheim,

gets taken out at Anaheim and percolated into the ground,

and becomes the drinking water of the city of Anaheim,

completing the trip from the sewers of Riverside County

to the drinking water supply of Orange County.

Now, you might think that this idea of drinking wastewater

is some sort of futuristic fantasy or not commonly done.

Well, in California, we already recycle about 40 billion gallons a year

of wastewater through the two-stage advanced treatment process

I was telling you about.

That's enough water to be the supply of about a million people

if it were their sole water supply.

The third tap that we need to open up will not be a tap at all,

it will be a kind of virtual tap,

it will be the water conservation that we manage to do.

And the place where we need to think about water conservation is outdoors

because in California and other modern American cities,

about half of our water use happens outdoors.

In the current drought,

we've seen that it's possible

to have our lawns survive and our plants survive

with about half as much water.

So there's no need to start painting concrete green

and putting in Astroturf and buying cactuses.

We can have California-friendly landscaping with soil moisture detectors

and smart irrigation controllers

and have beautiful green landscapes in our cities.

The fourth and final water tap that we need to open up

to solve our urban water problem

will flow with desalinated seawater.

Now, I know what you probably heard people say about seawater desalination.

"It's a great thing to do if you have lots of oil, not a lot of water

and you don't care about climate change."

Seawater desalination is energy-intensive no matter how you slice it.

But that characterization of seawater desalination

as being a nonstarter is hopelessly out of date.

We've made tremendous progress in seawater desalination

in the past two decades.

This picture shows you

the largest seawater desalination plant in the Western hemisphere

that's currently being built north of San Diego.

Compared to the seawater desalination plant

that was built in Santa Barbara 25 years ago,

this treatment plant will use about half the energy

to produce a gallon of water.

But just because seawater desalination has become less energy-intensive,

doesn't mean we should start building desalination plants everywhere.

Among the different choices we have,

it's probably the most energy-intensive

and potentially environmentally damaging

of the options to create a local water supply.

So there it is.

With these four sources of water,

we can move away from our reliance on imported water.

Through reform in the way we landscape our surfaces and our properties,

we can reduce outdoor water use by about 50 percent,

thereby increasing the water supply by 25 percent.

We can recycle the water that makes it into the sewer,

thereby increasing our water supply by 40 percent.

And we can make up the difference through a combination

of stormwater harvesting and seawater desalination.

So, let's create a water supply

that will be able to withstand any of the challenges

that climate change throws at us in the coming years.

Let's create a water supply that uses local sources

and leaves more water in the environment for fish and for food.

Let's create a water system that's consistent with out environmental values.

And let's do it for our children and our grandchildren

and let's tell them this is the system

that they have to take care of in the future

because it's our last chance to create a new kind of water system.

Thank you very much for your attention.

(Applause)