Image copyright Thinkstock

Researchers at Imperial College London made headlines last year when they claimed that up to 200 litres of water could be involved in the download of a single gigabyte (GB) of data.

It's a shocking statistic - especially when you consider that in 2015 alone the average western European smartphone user got through 1.9GB of data per month per person - rising to 3.7GB per month in the US according to a report by Ericsson.

That's an awful lot of water.

Whenever you check social media, send an email, or stream a video, you will be receiving and exchanging data with a data centre somewhere in the world - a vast server farm full of heat-producing, power-hungry computers.

It's how our data travels with us - the reason you can log on to your email account on any device, wherever you are in the world, is because your emails are not stored on a hard drive owned by you.

What's that got to do with water? The Imperial College researchers calculated that it is probably either used in the vital process of keeping the data centres cool, or further away from the front line, in the production of the large amounts of electricity required to keep the centre operational.

Image copyright Green Mountain Image caption Computer servers require constant cooling

But before you throw your wi-fi out of the window, a note of caution from one of the Imperial College researchers, Bora Ristic.

He told the BBC at the time there was "a wide range of uncertainty" in the figure, and that it could be as low as one litre per gigabyte - but what the work did was to highlight that the water footprint of data centres has been sorely under researched.

"It's really useful preliminary research starting to scope the problem," said tech expert Bill Thompson on the BBC's Click Radio programme.

"It's very unlikely to change consumer behaviour, what you want to do is change the behaviour of the people running the data centres.

Image copyright Microsoft Image caption Microsoft hopes underwater data centres will be viable

"I can't see myself not streaming a video just because I'm worried about the water consumption. I can see me choosing a video hosting service that says, 'we are environmentally aware'."

Kaveh Madani from the Centre for Environmental Policy at Imperial College says that things have improved since the research was carried out.

"Facebook, Apple, Microsoft and Google have made substantial improvements with respect to their water footprint," he says.

"They are investing in this area because they appreciate water availability issues. They also understand the reputational risk better than before. If they overlook their environmental effects, they can hurt their reputation."

However as the demand for data centres continues to grow, so do the environmental issues.

Mr Madani adds: "Increased service requires additional energy use and heating. Additional energy use and heating means more environmental impact, carbon footprint and water use.

"There is a serious need for technology improvements in this section."

Naturally cooled

Green data centres may sound like an anomaly by their very nature - but it is a commitment taken seriously by many of the world's leading tech firms.

Whether it's by using renewable power, or choosing to locate their data centres in environments that naturally lend themselves to the cooling process, here's how some of them are giving their green credentials a boost.

Image copyright Facebook Image caption Facebook's Lulea data centre is located just south of the Arctic Circle

In February 2016, Microsoft finished testing its first prototype underwater data centre, the concept being that the surrounding water keeps the centre cool rather than requiring energy draining air conditioning or alternative cooling mechanisms.

Facebook opened its Lulea data centre near the Arctic Circle in the north of Sweden in 2013 for a similar reason - the cold temperatures provide a natural cooler. That centre now employs 150 staff and is 100% hydro-powered. Naturally, it has its own Facebook page.

The firm has also started building a massive 57,000 sq metre data centre campus in Clonee, in the Republic of Ireland, which it says will be 100% wind-powered, like similar bases in Fort Worth and Altoona.

Meanwhile, data centre firm Green Mountain took over a former NATO ammunitions storage facility inside a Norwegian mountain - it says it uses water from the surrounding fjord, which has a consistent eight degree temperature, to keep its plant cool, requiring no extra energy.

Apple has also been moving increasingly into green power, saying that all of its data centres are now 100% renewably powered.

And this month Google announced that six of its data centres are now creating no landfill rubbish at all.

"Globally across our data centre operations we are diverting at least 86 percent of waste away from landfills," wrote Rachel Futrell, a Google technical program manager, in a blog post.

Wind farms

Greenpeace's Clean our Cloud campaign has been fairly quiet for a while, but a new report is due out next month, says analyst Gary Cook from the environmental group.

"Companies have redefined the art of the possible - we can run very big things on renewable energy," he says.

Image copyright Getty Images Image caption Amazon has been investing in wind farms

"The big firms are opening doors for others to tap into renewables - we've seen this a lot in the US in the past 3-5 years."

While Mr Cook is broadly supportive of the steps taken by the giants, there is one company he singles out for criticism - Amazon Web Services.

"Amazon's growth is five or six times larger than the amount of renewables they have brought onto the grid," he says.

"They have started to move - but we'd like them to be renewably powered, more transparent."

Amazon says it has a "long term commitment" to run its infrastructure on 100% renewable energy.

It hopes to achieve 40% by the end of 2016, it says on its website.

Amazon also owns three wind farms and one solar farm in the US, which it claims generates enough electricity to power 150,000 homes.