Shoppers in Amsterdam are being encouraged to donate their wee in a set of portable urinals, set up in the city's bustling Beursplein square.
It's all part of a campaign which aims to create a hectare of 'living roofs' in the city, with the aim of making the city number one for urban greenery.
Phosphates from the wee will be extracted, and used to fertilise the plants in a network of roof gardens.
Human urine is chock full of nitrogen, potassium and phosphorus - all nutrients plants thrive on and the main ingredients in modern fertilisers.
Phosphorus is usually mined from phosphate rocks to make crop fertilisers, but experts think natural supplies will run out in the next 100 years.
The plan - dubiously dubbed Green Urine - is part of International Water Week, a biannual event focusing on environmentally sustainable solutions to water supply and sanitation.
- Mirror
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