Urine was used as fertiliser in ancient Rome and China. Now farmers in Vermont are bringing this practice back to boost harvests and grow crops in a more sustainable way.

When Betsy Williams goes to the loo, she likes to know her pee won't go to waste. For the last 12 years, she and her neighbours in rural Vermont, US, have diligently collected their urine and donated it to farmers for use as fertiliser for their crops.

"We're consuming all of these things that have nutrients in them, and then a lot of the nutrients that are passing through us can then get recycled back into helping create food for us and for animals. So to me, it's logical," Williams says.

Williams takes part in the Urine Nutrient Reclamation Program (UNRP), a programme run by the Rich Earth Institute (REI), a non-profit based in Vermont. She and 250 of her neighbours in Windham County donate a total of 12,000 gallons (45,400 litres) of urine to the programme each year to be recycled – or "peecycled".

Windham County's pee-donations are collected by a lorry and driven to a large tank where the urine is pasteurised by heating it to 80C (176F) for 90 seconds. It is then stored in a pasteurised tank, ready to be sprayed on local farmland when the time is right to fertilise crops.

Records suggest that urine was used to help grow crops back in ancient China and ancient Rome. Today, scientists are finding that it can more than double the yield of crops like kale and spinach compared to no fertiliser, and improve yields even in low fertility soils.

Urine's power as a fertiliser is due to the nitrogen and phosphorus that it contains – the same nutrients that are added to the synthetic fertilisers used on many conventional farms. But these synthetic fertilisers come at an environmental cost. Nitrogen is produced using the fossil fuel-intensive Haber-Bosch process, and the mining of phosphorus creates harmful amounts of toxic waste. Urine, meanwhile, is freely available – as Williams puts it, "everybody pees. [It's an] untapped resource".

Nancy Love, a professor of civil and environmental engineering at the University of Michigan who has collaborated with the team at REI over the last decade, has found that using urine instead of standard synthetic fertiliser reduces greenhouse gas emissions, and requires around half the amount of water. Indeed, since 2012, UNRP estimates that it has conserved over 2.7 million gallons (10.2 million litres) of water through preventing toilet flushes.

"I've always been a systems thinker, and our [water] system has inefficiencies in it," Love says. "What we do today is dilute the hell out of our urine, we put it in a pipe, we send it to a treatment plant, and then we pump a bunch more energy into it, just to send it back into the environment in a reactive form."

In the case of urine's nutrients, its typical destination is waterways. The nitrogen and phosphorus in urine are not fully removed from wastewater when it is treated. When these nutrients find their way into rivers and lakes, they are taken up by algae. The result can be algal blooms that choke up waterways, unbalancing the ecosystem and killing other species that live there.

"Our bodies create a lot of nutrients, and right now those nutrients are not only wasted, but they’re actually causing a lot of problems and harm downstream," says Jamina Shupack, REI's executive director.

These nutrients are food for algae – but also for crops. "Wherever you put nitrogen, it's going to help plants grow. So if it's in the water,........

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