Should you pee on your crops? It's a serious question. Take a close look at urine and you will find it contains most of the nitrogen and phosphorus we excrete – two of the three main nutrients used in fertilisers. Yet fertilisers are mostly produced through energy-intensive methods, and many African countries have to import them. Even worse, phosphorus has to be mined, and we may be running out of it sooner than oil. Re-using nutrients from urine would make a lot of sense, and there are several active research projects on that topic, many of which are just as energy-intensive and therefore expensive as traditional production methods. At WaterAid, we wanted to find solutions that would be typically affordable and make sense for farmers in sub-Saharan Africa. Gold in Mozambique In Mozambique, WaterAid has been promoting ecological sanitation for some time, through composting toilets that separate faeces for compost and urine (see our technology poster for more details). With composting toilets, urine is typically left to infiltrate in the ground and can create unpleasant smells, which is a common reason for not using them. But a recent project has been transforming behaviours in peri-urban Maputo to promote the direct reuse of urine on vegetable gardens by diluting it with water. The following short film, which recently won a Social Impact Media Award, describes how urine has become the ‘gold’, providing substantial benefits to crops: Solar heating experiments in the UK One limitation mentioned by the project participant in the film is the low volume that can be used, limiting this application to relatively small gardens. We wondered if another way was possible, so we ran a competition in 2013 together with the Society of Public Health Engineers. The winners suggested a solar heating system that could pasteurise urine, evaporate water and allow urea to be extracted and reused as fertiliser. After a trip to Tanzania to test the feasibility, young engineer Paul Foulds worked hard to develop a prototype. Read the report > He managed to extract urea (despite solar heating being much less efficient in the UK), but ran into issues with keeping the urea dry. We therefore worked with students in Water and Environment at Cranfield University, who, after a few months of testing different setups and evaporation methods, managed to extract urea. The urea was in very small quantities, which seemingly indicated that this wouldn't be a commercially viable method. However, the students have some ideas that could help the process, which we could continue testing in the future. We are grateful to competition winner Paul Foulds, to Cranfield lecturers Drs Alison Parker and Kristell Le Corre Pidou, and to Cranfield students Alexander Hunter, Colette Génevaux, Louisa Fearn and Raphaël Formarier for their very helpful work. Oh, and to answer the question: yes, you can reuse urine, as it is sterile (unless you're on medication). But be sure to dilute it or you will kill your plant with too much nitrogen. More practical tips this way! Read the report: Optimisation of a low-cost urine treatment system for resource recovery > The 2015 Young Engineers Award from the Society of Public Health Engineers (SOPHE) is now open, with two very unusual challenges. The award is open to all engineers, and the winning team will have the opportunity to test the viability of their design on an in-country trip. Full details can be found here > Rémi Kaupp is WaterAid’s Programme Officer, specialising in urban sanitation. He tweets as @RemKau and you can read more of his blog posts here. For global policy, practice and advocacy updates and discussion, follow @wateraid on Twitter.