Plants need phosphorus, and we are running out of the stuff; some say we will reach peak phosphorus by 2030. That's we should recycling urine, to recover the phosphorus in it instead of flushing it away.
Rich Heap of Future Cities describes how Amsterdam's water utility, Waternet, has set up a demonstration project to collect urine, (in these very public urinals), separate the struvite (April explains how that's done in Sweden) and will use this to fertilize a few acres of green roof. And while the question of peak phosphorus is controversial,
...even if there isn't a looming shortage, cities can still look at ways to extract more value from urine. It may also help protect them against fluctuating fertilizer prices.
This is why Waternet is looking to extract more phosphates from urine and sewage. Construction started in September on a processing plant that is due to open in 2014, including a collection point for pure urine. It says wastewater from 1 million people in Amsterdam could enable it to produce 1,000 tonnes of fertilizer each year.
Really, we should be doing this everywhere. We should all be selling our pee instead of paying taxes and water bills to flush it away.