Water is essential for life, but too much of it can have a detrimental effect on the environment. Excessive water can reduce oxygen levels in the soil, leading to root loss or injury and making plants more susceptible to fungal diseases. Heavy rains can also cause soil compaction and erosion. Surface waters and aquifers can be contaminated by a variety of chemicals, microbes and radionuclides.
Drinking water disinfection has been successful in reducing the prevalence of waterborne diseases in the United States, but other processes are also used to treat drinking water depending on the characteristics and contaminants of the water source. Flood water can contain waste, pollutants and nutrients, as well as debris such as trees and stones, or even pieces of houses. Contaminants from flood water, such as bacteria and pesticides, can be transported over long distances. Sedimentation and turbidity can cause the growth of algae and phytoplankton that endanger water quality.
Transboundary pollution is the result of contaminated water from one country being spilled into the waters of another. When water pollution causes algae to grow in a lake or marine environment, the proliferation of newly introduced nutrients stimulates the growth of plants and algae, which in turn reduces oxygen levels in the water. The EPA presents a drinking water indicator based on drinking water standard violations that states report to them. Watersheds in urban areas with lots of concrete, pavement, and roofs shed water quickly, while rural wooded and grassy areas absorb more water.
Nutrient pollution, caused by excess nitrogen and phosphorus in water or air, is the main threat to water quality around the world and can lead to the proliferation of algae, a toxic blue-green algae soup that can be harmful to people and wildlife. In an effort to open the door to industrial waste and interstate disputes, the Ohio River Valley Water Sanitation Commission is making its water quality standards voluntary. Water managers use this information to make decisions about water allocation, such as how much water should be released from a reservoir during spring runoff. Virtually all drinking water in the United States comes from fresh surface water and groundwater aquifers.
Surface water from freshwater sources (that is, from sources other than the ocean) represents more than 60 percent of the water supplied to U. S. homes. Water pollution occurs when harmful substances (often chemicals or microorganisms) contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading its quality and rendering it toxic to humans or the environment. Agriculture is not only the biggest consumer of global freshwater resources - since agricultural and livestock production uses about 70 percent of Earth's surface water supplies - but it also seriously pollutes our waters.