Image caption Sara Plaza has lived beside the vast salt flat all her life

Out of habit, Sara Plaza smiles when her photo is taken, but when she talks about what has happened to the land around her home, tears start to run down her face.

"There used to be beautiful lagoons down there, with hundreds of flamingos," she says. "When they opened their wing, you'd see their pretty pink and black feathers. Now it's all dry and the birds have gone."

Peine, the dusty village where she lives in northern Chile, sits on a hillside by the Salar de Atacama, an enormous 3,000 sq km (1,200 sq mile) salt flat in the driest desert on the planet.

Sara says that the villagers used to graze their animals on pastures on the edge of the Atacama, beneath the giant Andes mountains.

Image caption The Salar de Atacama covers a huge area

"It used to be so green, now it's just hard, cracked ground. We can't keep llamas anymore," she laments.

Sara says that lithium mining on the Atacama is using up all the fresh water in the region's aquifers - layers of porous rock beneath the soil which act as stores of water.

Lithium, a soft, silvery-white metal is used to make batteries for smartphones, laptops and electric cars. Demand has soared in recent years, with global output rising three-fold since 2005 to 85,000 tonnes in 2018, according to the US Geological Survey.

Chile is the world's second-largest producer after Australia, with an output of 16,000 tonnes last year, all from the Atacama. Valued at $949m (£785m) this was a 38% rise on 2017.

There are currently just two companies mining lithium here - a US firm, Albemarle, and Chile's own SQM.

Beneath the salt flat is an enormous natural underground reservoir of salty water that contains dissolved lithium salts. To extract this, the miners pump this brine to the surface, and allow it to evaporate in the sun, leaving the lithium carbonate to be scooped up. This salt can then be turned into metallic lithium.

Image copyright Reuters Image caption Albemarle and SQM pump brine into basins to extract lithium

While there are continuing concerns about the impact the extraction of this salt water is having on the wider ecosystem, including the claims that the flamingos' salt water lagoons are drying up, the most pressing issue for Sara and other locals is that the mining firms are also accessing fresh water supplies.

They need the fresh water to clean machinery and pipes, and also to produce an auxiliary product from the brine - potash - which is used as a fertiliser.

Standing among yellowing tufts of grass that used to be pasture lands Sarah - who monitors water supplies for her indigenous community - points out a small pumping station that draws up underground fresh water and pipes it to the lithium mines.

About 40km (25 miles) further north, Jorge Cruz grows maize and alfalfa on a small plot of land in the village of Camar, another indigenous community near the salt flat.

He says that if the mining companies continue to use fresh water at the current rate his village will not survive.

"The birds have gone, we can't keep animals anymore," he says. "It's getting harder and harder to grow crops. If it gets any worse... we will have to emigrate."

Diego Hernandez, president of the Chilean mining society, Sonami, says that the amount of fresh water used by the lithium companies is insignificant. But he does agree that all water levels should be better monitored by the authorities.

Image caption Jorge Cruz says he can no longer farm animals because of the lack of fresh water

"The government has no hydrological model of the whole aquifer," he says. "It should be able to take informed decisions based on technical data. But in Chile we have more rules and laws than money to make it happen."

Both Albemarle and SQM do their own monitoring of the ground water.

Global Trade

More from the BBC's series taking an international perspective on trade:

"We have the most advanced tools in the industry to monitor the health of the Salar de Atacama," says Eric Norris, Albemarle's president.

All of Albemarle's measurements are available to the authorities and to local communities, he adds. And the firm's engineers are working on new technologies to produce greater amounts of lithium using less water, because they are aware of the need to manage the region sustainably.

Image caption Chile exports nearly $1bn worth of lithium a year

"We're highly invested in protecting this ecosystem," he says.

Both companies have quotas for the amount of water they can extract each year. However, each has at times suggested the other is breaching those limits.

Albemarle says it is authorized to pump 442 litres per second of brine, and 23.5 litres per second of fresh water.

Alejandro Bucher, SQM's vice president of environment, says his company is also committed to carrying out its operations in a sustainable manner.

But he says the Atacama's ecosystems are extremely dynamic, and show important variations from year to year. Mr Bucher adds that observers should not interpret these variations as permanent changes to the local environment.

"Our long term environmental monitoring, which is evaluated regularly by the environmental authorities, shows that the ecosystems are intact, including areas of vegetation, lagoons and flamingo populations," he says.

Image caption Sara says that the two mining companies use pumps such as this to access fresh water

Some government bodies are expressing concern, however, including state development agency, Corfo.

It found last year that more fresh water and brine was leaving the system through pumping and evaporation than was coming back in via rain and snowfall. But it couldn't pinpoint whether lithium or copper mining were specifically to blame. The copper mines, more than 80km away, are accessing the same sources fresh water and piping it to their facilities.

Local groups would like a more joined-up approach to managing Atacama's water, and want the government to ensure nearby communities have enough fresh water for farming and their own consumption.

"The [current] level of water extraction is causing real harm to the ecosystem and nearby communities," says Gonzalo Pimentel of the Atacama Desert Foundation, a non-profit institution supporting local communities.

Image copyright Getty Images Image caption Flamingos, which nest in the region, are said to have become much less common on the salt flat

What won't happen though is any brake on the lithium mining.

Several international companies are in talks with the government about licences to join Albemarle and SQM in extracting more of the valuable element.

Pro-government congressman, Guillermo Ramirez, says that as a mining country, Chile has long had to balance citizens' needs for water with the demands of the industry.

He says that the government will always act to ensure communities have water, and the key is good regulation of the mining industry. Nevertheless, he believes the potential of lithium is too valuable to ignore.

But Sara is fearful. "We'll be left here with no water, no animals, no agriculture - with nothing."