The Yellow River is at its lowest level in 50 years and millions in northern China face water shortages this summer. Chinese officials reported that more than half the watersheds of China’s seven major rivers are contaminated, with pollution levels in the Yellow River at or beyond China’s worst measurement. Only a quarter of China’s household sewage is treated, and virtually all of that is in cities, so rural water pollution is endemic and serious. Officials acknowledge that the air is polluted in two-thirds of China’s cities.