What Is Water Pollution? Sources, Environmental Impacts, Mitigation

Water pollution is defined by any contaminants discharged into aquatic ecosystems that lack the capacity to absorb or remove them. This encompasses contamination from physical debris, such as plastics or rubber tires, as well as chemical contamination, such as when runoff finds its way into waterways from factories, farms, cities, and cars. Biological agents, such as bacteria and viruses, can also contaminate water. 

All life on Earth relies on water, which means water pollution and all its sources are very real threats to our ecosystems. Here, we uncover where water pollution comes from, how the varying types affect the world's aquatic ecosystems, and what organizations and civilians alike can do about it.

Water Sources Subject to Pollution

There are two separate sources of water on our planet at risk of pollution. First is surface water—think oceans, rivers, lakes, and ponds. This water is home to many plant and animal species that rely on good-quality water for their survival. No less important is groundwater, which is stored below the surface in the Earth's aquifers, feeds our rivers and oceans, and forms much of the world's supply of drinking water. 

Surface water and groundwater can become polluted in a number of ways, and here it helps to understand how pollution types are often divided.

• Point source pollution refers to contaminants that enter a waterway via a single, identifiable source. Examples include a wastewater treatment pipe or a leaking oil pipeline. 
• Non-point source pollution comes from many scattered locations. Examples include nitrogen runoff from agricultural fields and stormwater runoff that carries contaminants from sewage systems, roadways, lawns, and industrial facilities into rivers, lakes, and oceans.

Groundwater, in particular, is affected by point and non-point source pollution. A chemical spill or pipeline leak can seep directly into the soil, polluting the water below. But more often than not, groundwater becomes polluted when non-point sources of contamination such as chemical-laden agricultural runoff enter aquifers.  

Environmental Impacts

The impacts of water pollution may seem obvious: environmental damage and ecosystem disruption. Yet there are different levels to the damage that can ensue, so it is important to dive in and identify the key areas and species affected.

Agricultural Waste and Nutrient Pollution

Each summer off the coast of Louisiana and Texas, scientists measure a dead zone—an area with insufficient oxygen to sustain marine life. The culprit: stream discharge containing high levels of nutrient pollution.

Nitrogen and phosphorus runoff from farm fertilizers and animal waste, along with other land-based pollutants like pesticides, flow into waterways that eventually feed into the mighty Mississippi and other major rivers, which then carry massive amounts of nutrients into the Gulf of Mexico.

These nutrients stimulate algae production. As the algae die, they sink and decompose, becoming food for oxygen-consuming bacteria. The low oxygen levels force many marine species to move, creating huge areas void of life. Dead zones also occur in aquatic and marine systems in other parts of the United States and around the world, including in the Chesapeake Bay and Great Lakes. Sometimes the algae itself is toxic, too, rendering water and even the surrounding air dangerous.

Industrial and Extractive Waste

Chemicals and heavy metals from industrial facilities and power plants, along with extractive industries like oil and gas drilling and mining, also contaminate water, often with devastating consequences. 

Power plant emissions account for 30% of water pollution from industrial sources in the United States. Heavy metals like lead, mercury, and arsenic don’t degrade. Instead, they concentrate as they move up the food chain, bioaccumulating in the bodies of fish, wildlife, and people.

Fossil fuel drilling and transport infrastructures like pipelines and tankers are other big water pollution sources. Hydraulic fracturing or fracking and conventional oil and gas drilling, along with wastewater storage and disposal, can contaminate aquifers. That has happened in California’s San Joaquin Valley, where toxic waste fluids from oil drilling operations have leaked or migrated into groundwater.

Pipeline accidents, like the 2010 oil spill in Michigan in which a broken Enbridge Energy Partners pipeline dumped a million gallons of crude oil into the Kalamazoo River, are common in the United States. Offshore drilling rig blowouts, like the 1969 Santa Barbara oil spill and the 2010 Deepwater Horizon disaster, along with tanker leaks like the 1989 Exxon Valdez oil spill have caused ecological disasters in marine and coastal ecosystems.

Wastewater

Wastewater refers to everything that goes down a drain or through a sewage pipe. Human waste contains not only bacteria and viruses, but pharmaceutical products, nutrients like phosphorus and nitrogen, and contaminants that we’ve consumed. Household cleaners, personal care products, and lawn and garden chemicals contribute additional chemicals and plastics to wastewater. 

While wastewater treatment systems filter some of these, even the most high-tech treatment facilities don’t remove every contaminant. And not all wastewater ends up in treatment systems. Aging and poorly managed septic systems, for example, leach untreated wastewater into the ground, directly contaminating surface and groundwater sources.

Stormwater runoff represents another threat. When rain and snow hit impermeable surfaces like concrete and roads that can’t absorb the precipitation, it flows instead to drains and surface waters, picking up pesticides, oil from roads, and lots of other chemicals. In addition, during heavy precipitation events, many wastewater treatment facilities release untreated sewage into waterways.

Plastic Pollution

Plastics pose another challenge as rapid production of disposable plastic products outpaces humanity’s ability to manage the waste. Significant amounts of plastic end up in waterways and eventually the world’s oceans. Plastic washes up on beaches, and joins the enormous gyres of waste that collectively make up the Great Pacific Garbage Patch.

Once in water bodies, plastic simply breaks into smaller and smaller components called microplastics. These microplastics end up in marine organisms, including fish that people consume, ingesting tiny particles of our plastic bags, water bottles, and synthetic clothing.

In addition to ingesting plastics, birds and marine life die from becoming entangled in fishing gear, six-pack can rings, and other plastic debris.

Climate Change

Climate change is both a contributor to water pollution and a consequence of it. Extreme weather like intense storms and drought worsen water quality, while warmer water temperatures encourage algal blooms and hinder the growth of native plants, like seagrasses, that sequester carbon, and filter contaminants. Carbon emissions are causing ocean acidification, which further impacts marine ecosystems and inhibits the ability of plants and animals to absorb carbon.

Climate change is also converging with water pollution to diminish the world’s drinking water supplies. Only by understanding the relationship between these problems and addressing them in tandem will the world avoid chronic, severe water crises.

How to Mitigate Water Pollution

Pollution caused in one part of the world can affect a community in another. But political boundaries make it difficult to impose any one standard to regulate how we use and protect the world's water.

Still, a number of international laws aim to prevent water pollution. These include the 1982 United Nations Convention on the Law of the Sea and the 1978 MARPOL International Convention for the Prevention of Pollution from Ships. In the United States, the 1972 Clean Water Act and the 1974 Safe Drinking Water Act, among other legislation, were created to help protect both surface and groundwater supplies. 

In addition, global actions to replace fossil fuels with renewable energy sources and mitigate the impacts of climate change on water supplies help combat water pollution. 

Despite these and other actions to protect water quality, some places lack the necessary infrastructure to achieve the standards. In other cases, a government may lack the resources or political will to regulate the industry and enforce pollution controls.