But according to EPA estimates, our nation’s aging and easily overwhelmed sewage treatment systems also release more than 850 billion gallons of untreated wastewater each year. These facilities reduce the amount of pollutants such as pathogens, phosphorus, and nitrogen in sewage, as well as heavy metals and toxic chemicals in industrial waste, before discharging the treated waters back into waterways. In the United States, wastewater treatment facilities process about 34 billion gallons of wastewater per day. More than 80 percent of the world’s wastewater flows back into the environment without being treated or reused, according to the United Nations in some least-developed countries, the figure tops 95 percent. The term also includes stormwater runoff, which occurs when rainfall carries road salts, oil, grease, chemicals, and debris from impermeable surfaces into our waterways It comes from our sinks, showers, and toilets (think sewage) and from commercial, industrial, and agricultural activities (think metals, solvents, and toxic sludge). Nutrient pollution, caused by excess nitrogen and phosphorus in water or air, is the number-one threat to water quality worldwide and can cause algal blooms, a toxic soup of blue-green algae that can be harmful to people and wildlife. Every time it rains, fertilizers, pesticides, and animal waste from farms and livestock operations wash nutrients and pathogens-such bacteria and viruses-into our waterways. It’s also a major contributor of contamination to estuaries and groundwater. In the United States, agricultural pollution is the top source of contamination in rivers and streams, the second-biggest source in wetlands, and the third main source in lakes. Around the world, agriculture is the leading cause of water degradation. Not only is the agricultural sector the biggest consumer of global freshwater resources, with farming and livestock production using about 70 percent of the earth’s surface water supplies, but it’s also a serious water polluter.
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