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Americans may face even more urgent problems from pollution. Drinking water in the United States is generally safe and meets high standards. Nevertheless, one in five Americans every day unknowingly drinks tap water contaminated with bacteria and chemical wastes, according to the Environmental Protection Agency. In Milwaukee, 400,000 people fell ill in 1993 after drinking tap water tainted with cryptosporidium (Òþæß×Ó³æ)£¬a microbe (΢ÉúÎï) that causes fever, diarrhea (¸¹Ðº) and  vomiting.

THE  SOURCE

Where so contaminants come from? In developing countries, people dump raw (δ¾­´¦ÀíµÄ) sewage(ÎÛË®) into the same streams and rivers from which they draw water for drinking and cooking; about 250 million people a year get sick from water borne (ÒûË®´«È¾µÄ) diseases.

In developed countries, manufacturers use 100,000 chemical compounds to make a wide range of products.Toxic chemicals pollute water when released untreated into rivers and lakes. (Certain compounds, such as polychlorinated biphenyls (¶àÂÈ»¯Áª¶þ±½)£¬or PCBs, have been banned in the United States.)

But almost everyone contributes to water pollution. People often pour household cleaners, car antifreeze, and paint thinners (Ï¡ÊͼÁ) down the drain; all of these contain hazardous chemicals. Scientists studying water in the San Francisco Bay reported in 1996 that 70 percent of the pollutants could be traced to household waste.

Farmers have been criticized for overusing herbicides and pesticides, chemicals that kill weeds and insects but insects but that pollute water as well. Farmers also use nitrates, nitrogen--rich fertilizer that helps plants grow but that can wreak havoc (