The environment, public health, and global political stability all stand to suffer from shrinking freshwater supplies around the world, according to a report released yesterday by the United Nations. In the most complete appraisal of global water resources to date, the U.N. found that the average per-person water supply will decline by one-third in 20 years, and as many as 7 billion people could face water shortages by mid-century. Developing nations and impoverished people will be hit hardest by the shortages, which are fueled by global warming, population growth, and poor management of water resources. The report was released one week in advance of the Third World Water Forum, where delegates from around the globe will converge in Kyoto, Japan, to try to develop strategies to protect water resources and forestall the kinds of crises (ranging from illness to war) that could stem from dwindling freshwater supplies.