Water is also a carrier of disease.
Most U.S. cities have deteriorating waste water treatment and distribution systems with completely inadequate programs for replacement or upgrade. Since the United States is one of the fastest growing industrial countries, municipal systems will be further strained. Previously unrecognized waterborne pathogens, such as Cryptosporidium, already have emerged. In the developing world, where 98 percent of population growth now takes place and is projected to take place, squalid urban slums are already crowded with an unprecedented number of displaced people living in conditions favorable to the rapid spread of disease. Water is essential for all living things.