Why we should all be astronauts
If you want to get a laugh out of a five-year-old, telling them that astronauts drink their own wee is bound to do the trick.
It's one of those fun facts that fascinates people about life in space.
Robyn Gatens, deputy division director for Nasa's International Space Station (ISS) programme, has seen plenty of negative reactions to the practice in her 30 years at the US space agency.
"It's a mental thing, it sounds yucky," she says.
The ISS recycles about 90% of all its water - as well as astronauts' urine, this includes their sweat, the moisture from their breath and their washing water.
"Yesterday's pee is this morning's coffee basically," is how British astronaut Tim Peake summed up the process.
A role model
It may sound unappetising, but the ability to reuse the same water over and over again has enabled people to stay in space longer without refuelling. Ultimately it could help astronauts become self sufficient on a planet such as Mars, a two-year trip Nasa says it is planning for the mid-2030s.
It is just one example of the many ways in which Nasa exploits limited resources. And it's exactly the kind of practice that makes the space agency a role model for those on earth trying to eliminate waste by reusing and repurposing things.
Nasa works with businesses on a lot of its research and has a Technology Transfer Program aimed at making sure its scientific know-how is applied on Earth as well as in space.
"We're working across industries, not just traditional space companies," says Ms Gatens.
US firm Water Security Corporation, for example, bought the rights to Nasa's water recycling tech and now uses a simpler version of it on earth.
The firm's filters are used to supply clean water in remote areas in countries such as Mexico and India, or disaster relief areas.
In Nasa's case, recycling almost all the water on the ISS has meant that since 2009 the space station has been able to host six astronauts, rather than three. This expansion has been "critical", says Ms Gatens, because it has enabled the crew to carry out more scientific research.
It's also saved a huge amount of money. Nasa last year estimated sending water to the space station, instead of reusing it, would have cost it more than $225m (£180m) due to the high cost of transporting such a heavy item.
But the space agency isn't stopping there. It's now working to recover even more water from the concentrated urine left behind by the current process. What's left after this will be solid waste that, Ms Gatens says, could potentially be used as radiation protection.
Nasa also recycles air on the ISS. Currently the space station's system recovers about half of the oxygen contained in the CO2 breathed out by the crew, a percentage it's actively trying to increase.
Start-up Skytree arose out of working on this technology. The firm's founders met at the European Space Agency (ESA) where they were working on recapturing CO2 to make longer space missions possible.
They secured funding from the ESA's technology transfer programme - which helps entrepreneurs starting businesses using space tech in a different field.
Now the firm is working with different companies on a variety of commercial uses for its technology, including using the CO2 captured to increase the yields derived from plant crops for purifying water and to create a clean domestic energy source.
"We hope to initiate a positive shift in people's perception: from CO2 as a potential problem to CO2 as an essential and incredibly versatile resource," Skytree says.
Just like in recent film The Martian where stranded astronaut Mark Watney grew potatoes, Nasa is also working on growing its own fresh vegetables in space. The project is aimed at eventually providing those on longer missions, such as to Mars, with a sustainable food source.
To grow the lettuce - eaten by US crew for the first time last year - Nasa used a collapsible unit packed with rooting "pillows", essentially mini grow bags, which contained the seeds, and coloured LED lights to enhance plant growth.
Similar farming systems where plants are stacked up on shelves to save space and grown from seeds are already common in Asia, and are beginning to become more popular in the US and UK.
Dr Gioia Massa, a Nasa scientist working on food production, says many of the lessons the space agency is learning could be applied in urban plant factories and other agriculture settings, with the potential to increase the amount of food grown in less space. Such skills will be vital as the world's population increases.
But sustainable solutions are not always hi-tech. Currently, space farers enviably never have to wash their clothes, but simply throw them away at the end of their usable life.
ISS crew are now testing exercise clothing, which has been treated with an antimicrobial compound, enabling them to be worn longer without smelling.
The other solution being considered is a simple ozone washing machine which, as Ms Gatens notes, nurseries often use to wash toys.
But in other areas of sustainability Nasa still has a long way to go. For example, as well as used clothing, astronauts still throw away things such as empty containers and the material used to cushion cargo from vibrations.
The items are stored in cargo resupply ships, which then burn up upon re-entry to Earth's atmosphere, incinerating everything.
The space agency is now considering making the cargo cushioning material out of 3D printer stock so that once in space, it can be used to create things such as tools.
Another option is heating and compacting its rubbish. After hiving off the additional water, the process creates big plastic dishes, which Ms Gatens likens to "a huge coaster". She says this could then be used as additional radiation protection, for example, in crew sleeping areas.
"The mindset is, with limited resources, whatever you can use, you want to be able to repurpose that," says Mary Hummerick, a Qinetiq North America microbiologist at Kennedy working on the project.