Job opportunities should be plentiful for environmental scientists and especially for hydrologists. There were 8,100 hydrologist jobs in 2008, and employment should grow more than 18 percent by 2018. The government has stepped up environmental regulations and has begun cleaning up contaminated and hazardous waste sites—all efforts that increase the need for hydrological research. Competition for openings is limited by the small number of universities and colleges that offer degrees in hydrology.
The figures are for the United States but I would predict that a career to do with water holds a lot of promise in any country. This is not a new observation. Sometime back Science Careers carried a lengthy article on hydrogeology careers and called them "recession proof".
Population pressures, water reallocation challenges between rural and urban consumers, climate change and past mismanagement of water resources means there will be plenty of work for hydrologists and hydrogeologists for decades to come.