Separating urine from the rest of sewage could mitigate some difficult environmental problems, but there are big obstacles to radically re-engineering one of the most basic aspects of life.
I briefly had a project called Pee on a Tree that got mocked and got no traction. This is why Earth is doomed: The simple solutions are derided while people overcomplicate things that don't have to be complicated.
Hoomans: Y'all fools deserve your fate and I shall say so in my dissertation for my degree in Human Studies when I get back to Vulcan.