of paradoxes, of conundrums,

and of water that it's there but you don't see it.

There's parts of the cities where you would never know

just by looking at them that there's any

water crisis around.

They have clean water 24 hours a day,

apparently just as abundant as it would be

in New York or something like that.

Then you have other parts of the city

where people are living

in very, very, extremely precarious water situations.

Low-income parts of Mexico City

and the people that live around it

are now facing a situation where they open the tap

and no water comes out.

It's a very tragic story of having

all of the water in the world and somehow ending up

being a city that today is on the list

of top 10 cities most likely to run out of water.

You have to do something, and so we do.

Enrique Lomnitz' hometown, Mexico City,

is in a water crisis that gets worse by the day.

He started social enterprise Isla Urbana

to stem the tide.

They design and build cheap and simple systems

that catch and clean rainwater.

There's nothing new about rainwater harvesting.

People have been harvesting rainwater

since they first opened their mouths

and looked up at the sky at the same time.

It seemed to us like a logical thing.

Just figure out how we can use this water

that we have available to us

as kind of like a first part of a larger solution.

It's a situation that affects women very particularly.

Mostly it's women who tend to be more

kind of in charge of managing the household

and basically their lives start circling

around these water issues.

Elizabeth is one of 11 people

living in this house on the edge of Mexico City.

She's also one of 2.5 million people

who don't have access to permanent and safe drinking water.

But going thirsty isn't where Elizabeth

and her family's problems end.

The economic implications of not having water

are very interesting, and the people that rely

on water trucks, for example,

they often have to have somebody at home

all the time to wait for a possible water truck arrival

so there's often someone that can't work at all.

They just need to always be at home.

What's strange about Mexico City, though,

is it isn't some barren desert.

It's wet. Really wet.

Here we'll have one hour

where it's like apocalyptic.

The sky is just falling and there's lighting and thunder

and rivers in the streets.

During the rainy season you will have floods.

Those floods can last for days.

Mexico City gets considerably more rain

than a city like London does, for example.

The question that comes to one's mind

is if we have so much water resources,

why do we have to be in such a bad situation?

The water crisis in Mexico City is a 400-year-old story.

Mexico City started off being a city on an island

in the center of a lake in this basin

high up in the mountains.

And over the course of 400 years,

basically the city has focused on draining

all of these ancient lakes out of the aquifer

and building a giant modern city in its place.

So where you had this 2,000-square-kilometer lake

you now have just city as far as the eye can see.

You see a lot of highways and a lot of avenues

and streets who have the name of rivers.

Those streets were actually rivers 50, 60 years ago.

To provide for its vast population

around 1,800 wells pump water out of the ground,

depleting the aquifer below.

But because the city's prone to deadly flooding

it's built a massive infrastructure

to get the water out quickly when it rains.

The result: not enough water filters down

to recharge the aquifer.

The loss of that water that you can actually see

is paralleled with the drying up of all of the aquifers.

We're just pumping and pumping and pumping water

out of the ground to the degree that, actually,

Mexico City is physically sinking.

More than 10 meters in the last century.

Monuments need steps added for people to reach them,

streets rise and fall, sinkholes open up the earth,

and the water from the ground isn't enough

to quench the city's thirst.

30% of its water is imported from outside the city.

But the infrastructure is so old and huge

not only is 40% of water lost through leaks,

but much of what does make it can become contaminated.

Many people end up spending a significant portion

of their income on expensive bottled water.

People don't trust the quality of the water

they get out of the grid even in areas

where it's actually quite good.

98 or so percent of the population doesn't drink tap water.

They buy water from purifiers, from these filter stores

that will fill your five-gallon jugs.

We're industrial designers, and honestly,

we were looking for problems to solve.

People just started telling us about water.

They started telling us about how

their water situation was getting worse and worse.

Isla Urbana installed their first system

here in Ajusco on the southern edge of the city.

It didn't take long for people to realize the benefits.

Little by little almost all of the neighbors

have started harvesting rainwater themselves.

We're working with communities

so that they can become self-reliant

in getting their own water supply

and securing their own water.

It needs to be as simple as possible.

Rain falls on the roof, goes through the gutters,

goes through the pipe, diverts the first volume,

goes into a tank, gets chlorinated,

you let the little bits of dust settle

and then you pump that water out

and give it just some simple filtration.

That water you can just connect directly

into your house's existing plumbing system

so you open a tap in the kitchen

and that's the rainwater that's coming out.

For families in these areas that are very,

very water-stressed, starting to harvest rainwater

can mean sometimes doubling the amount of water

that you actually have available.

95% or so of the water that's used in a household

is not for drinking, it's for everything else,

and so that's really where you wanna hit first

'cause that's where you're gonna make

the biggest first difference.

So we want to have our baseline system

be as affordable as possible, but designed in such a way

that you can add new treatment systems to it

so that you can eventually stop

having to buy drinking water as well.

The water, it's water, except it's just water

that's reaching your house via falling on you from the sky

instead of coming from the city's water grid.

We get usually between 700 and 1,000 liters

of water per year for every square meter of roof.

So if you have a house that has, say,

a 100-square-meter roof, it's not a huge house at all,

a house like that can get up to

around 100,000 liters of water per year.

The problem at that point becomes

they just don't have enough tanks to store it all.

Mexico City should be able to get

at least 20 to 30% of its water demand

through rainwater harvesting systems,

which is very significant.

It's an incredible amount of water.

Guaranteeing water goes way beyond

quenching thirst and saving money.

It could also save a city from itself.

You have health, economic,

social, political problems.

If you divide the amount of water

that gets into the network every second,

every inhabitant of Mexico City

should get 350 liters per day.

If the entire eastern part of Mexico City

runs out of water there's gonna be

incredible amounts of social friction

and discontent and political crises.

We all live in this valley. We all need to be okay.

The local government has recognized

the perilous position the city finds itself in

and last year invested in 10,000 of Isla Urbana's systems.

They plan to install 100,000 by 2024.

Many believe regenerating areas of nature

holds the key to protecting cities

from problems like water sustainability.

We're not going to be able to return

to the Aztec city in the middle of the lake.

That's gone.

But we can have a new water model for the city.

A model where we keep water, we have rivers,

we have small lakes, and water can be a friend and an ally

and not a foe like it's today.

When it comes to running out of water,

Mexico City isn't alone.

L.A., Cape Town, Sao Paulo, the list is growing,

each with millions of inhabitants

facing devastating water crises.

They're serving as a warning

as more of the world's population migrates to urban centers.

Mexico City in 1940

had maybe a 1.5 million inhabitants

and today has close to 23 million people.

And this incredibly violent growth

and all this incredibly fast expansion of the city

has put unbelievable stress on all of the natural systems

that provide us with things like water.

Since 2009 Isla Urbana have installed

more than 20,000 of their harvesting systems,

mostly on top of low-income homes in Mexico City

and in rural communities.

Their devices catch a combined 800 million liters of water

each year, providing some 120,000 people

with a significant portion of their water needs.

I believe a lot in the

empowerment aspect of this.

How do we transition to being a society

where everybody is actively participating

in water management and is actually harvesting

their own water and taking care of it

and not relying on this other system?