It has begun. Government money is starting to flow into water sustainability here in Australia, and we are starting to see the emergence of real jobs in the area.
Because water has so many aspects, and any kind of water resource has a gazillion stakeholders, water sustainability is inherently a cross-disciplinary pursuit. You must cross-over the natural and engineered water-cycles and hence have a working knowledge of both hydrology/hydrogeology and civil/chemical engineering. You have to know behavioural science, economics and finance, advanced project management techniques, water science and urban planning.
I already have job opportunities for these people, so if you are one then get in touch!