Water Pollution

Water's direct impacts on human health come mainly from contaminants, which can be placed into broad classes: 

• Chemical contaminants: natural or human-created chemicals, and the focus of this page
• Biological contaminants: microbes including bacteria, viruses, protozoa, fungi, algae, amoebas, and slime molds
• Radiological contaminants: radiation from decaying radioactive elements, both naturally occurring from soil and bedrock and from radioactive waste deposited or leaking into water supplies

Thermal contamination, excess heat that impairs a water ecosystem's ability to sustain its lifeforms, is also a class of contamination. Although heat can impair an ecosystem's ability to produce food and other valuable services to humans, its direct impacts on human health are minimal.

Most health issues arise from inadequate access to clean water and from chemical contaminants.

Access to Enough Clean Water

According to a 2017 report from the World Health Organization (WHO) and the United Nations Children’s Fund, 844 million people still lacked even a basic drinking water service—an improved source within a 30-minute round trip from home—in 2015. An "improved" water source provides water when needed and is free from contamination, primarily microbial contamination from human or animal feces. That's almost 12 percent of the world population without access to clean water at home when it's needed. Of the 10 countries where at least 20 percent of the national population lacks basic water service, eight are in sub-Saharan Africa and two are in Oceania.¹⁵ Water supplies in some areas are being depleted or becoming unpredictable with climate change, slowing or reversing past progress in providing water access to communities.¹⁶

In the US, the 1974 Safe Drinking Water Act (see below) regulates drinking water systems that serve at least 25 individuals, and its implementation has made microbial contamination a rare occurrence in these systems. However, private and small community wells are not regulated or generally tested. A US Geological Survey report of testing in 48 states between 1991 and 2004 found that microbial contaminants were detected in as many as one-third of these wells.¹⁷

Chemical Pollution in Drinking Water

Chemical contaminants from both natural sources and human activity can make water unsafe or even unusable. Chemical contamination of water is a concern in many parts of the world, with the specific chemicals and their sources varying from one place to another. Some concerning facts and trends:

• In developing countries, 70 percent of industrial wastes are dumped untreated into waters, polluting the usable water supply.¹⁸
• Globally, the most prevalent water quality problem is eutorphication, an excess of nutrients (mainly phosphorus and nitrogen) in a body of water, frequently due to runoff from land. Agricultural fertilizer and animal/livestock waste are the main contributors to this situation, which causes dense growth of plant life and death of animal life due to lack of oxygen. Eutrophication can lead to algal blooms, "red tides", "green tides", fish kills, inedible shellfish and blue algae, substantially impairing use of water for drinking, food harvesting, cleaning and recreation.¹⁹
• A survey of 38 streams across much of the US in 2012-2014 found hundreds of chemical contaminants related to human activity, with the 10 most common being eight pesticides, caffeine and the diabetes drug metformin. Each of these contaminants were detected in 26 to 32 of the 38 streams.²⁰
• More than one in five US domestic wells tested from 1991-2004 contained one or more contaminants at a concentration greater than a human-health benchmark.²¹
• The drinking water of more than four percent of US residents exceeds the EPA’s maximum contaminant level of nitrates, most frequently in wells in agricultural areas.²²

• Plastics in Water Although direct impacts on human health are not yet widespread, the volume of plastic in surface water is enormous and growing exponentially.23 Many plastic monomers are classified either as carcinogenic, mutagenic or toxic for reproduction. Other compounds—such as solvents, initiators, catalysts and other polymerization additives, plus additives including flame retardants, phthalates and lead compounds—may be added to plastic during production.24 Plastic pieces already contaminate fish and seafood, introducing plastic directly into the human food supply.

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  About 4 million to 12 million metric tons of plastic washed offshore in 2010 alone, enough to cover every foot of coastline on the planet.²⁵
• All 50 states and some US territories and tribes have consumption advisories to protect people from potential health risks of eating contaminated fish caught in local waters. Ninety–four percent of advisories in effect in 2011 involved five bioaccumulative chemical contaminants: mercury, PCBs, chlordane, dioxins, and DDT.²⁶
• In 2015, at least 18 million Americans—and potentially many more—were served by water systems with lead violations. Testing over a four-year period from 2012 to 2016 showed excessive levels of lead contamination in almost 2,000 water systems in all 50 US states.²⁷
• A 2016 study found that levels of polyfluoroalkyl and perfluoroalkyl substances (PFASs)—a widely used class of industrial chemicals linked with cancer and other health problems—exceed federally recommended safety levels in public drinking-water supplies for 6 million people in the United States.²⁸
• A 2016 report found that chromium-6, a Class 1 carcinogen (known to cause cancer),²⁹ contaminates water supplies of more than 218 million Americans in all 50 states.³⁰ An update in 2017 raised the number of people affected to at least 250 million.³¹
• Fossil-fuel burning power plants discharge at least 5.5 billion pounds of pollution into US rivers, streams, lakes and bays each year. Coal-burning plants in particular discharge some of the most dangerous heavy metals on earth, including arsenic, lead, mercury, cadmium, chromium and selenium.³²
• Despite improvements in some regions, water pollution is on the rise globally.³³

Most chemicals in concentrations found in drinking-water supplies do not cause immediate harm, although there are some exceptions, such as nitrates in certain populations. Many chemical contaminants can contribute to or cause adverse health states from prolonged exposure.³⁸ Main sources of chemical contamination in US drinking water are industrial, agricultural, and municipal chemicals.³⁹

The specific contaminants can vary widely from one industry to another. This table presents common chemicals found in water, some of their main sources and health impacts. The health impacts are from our Toxicant and Disease Database unless noted otherwise. See About the Toxicant and Disease Database for a description of Strong Evidence and Good Evidence. Linked text in the table relates to pages on this website with more information.

Besides from human sewage,⁶² microbial contamination typically derives from agricultural activity, primarily livestock waste (sewage). Wildlife waste can also contaminate water. Waste can introduce pathogens such as Shigella, Salmonella, Cryptosporidium, Giarida, Legionella, and coliforms into drinking water, leading to diarrhea and gastrointestinal illness.⁶³ Cholera, caused by the bacterium Vibrio cholerae, is a particularly deadly water-borne disease; the World Health Organization reports about 1.3 to 4.0 million cases and 21,000 to 143,000 deaths worldwide every year from cholera, mainly in developing countries.⁶⁴ Increased runoff from land sources during heavy rainfall can lead to disease outbreaks. Waste can also cause algae blooms in surface water sources.⁶⁵

Both water scarcity and excessive water can impact health.

Water Scarcity

Even in areas with normal rainfall, water scarcity is becoming a concern—or already has become a concern. According to the World Wildlife fund, more than a billion people worldwide lack access to water, and a total of 2.7 billion find water scarce for at least one month of the year.⁶⁶ Water scarcity has many causes:

• Water availability is being limited in many places by drought, which can reduce drinking water and an area's ability to produce food crops and livestock.⁶⁷  
• Unsustainable water use is driving aquifer depletion and stress on watersheds worldwide. Agriculture uses 70 percent of the world’s accessible freshwater, but more than half of this is wasted due to poor decisions such as crop production in areas not suited to the crops' water needs and inefficient watering methods. Leaky irrigation systems also waste water.⁶⁸
• The growth of the human population puts extra pressure on water supplies. Deforestation, ultimately driven largely by population growth, also contributes to water degradation and reduced supply.⁶⁹
• As described above, pollution of water sources with chemical, radiation, microbial and other contaminants can make water unusable.⁷⁰

Excessive Water

In addition to causing tremendous disruptions in quality of life (and possible mental health impacts), heavy rainfall and floods can each increase water contamination by bringing pathogens and chemicals from roads, land, and buildings into water supplies. Excess water can also promote mold growth and increase populations of insects that transmit disease. Heavy rain and floods can also erode soil and reduce its future use in agriculture.⁷¹

The health and functioning of the world's oceans directly impact humans' health and existence:⁷²

• Oceans provide the majority of protein to more than a billion people.
• Phytoplankton, including microalgae, are responsible for greater than 50 percent of global primary production, including oxygen.
• Oceans store carbon, keeping it out of the atmosphere.
• Oceans modulate the climate, absorbing heat and transfering it around the world.

Oceans are threatened by many factors:⁷³

• Acidification
• Climate change's impacts on currents and carbon storage
• The depletion of species and disruption of ecosystems
• Chemical, nutrient and plastic pollution; the Great Pacific Garbage Patch (which is only the largest of several garbage patches in the oceans) and the New-Jersey-sized dead zone in the Gulf of Mexico are just two examples of situations where ocean functioning is grossly impaired by human activity.

In the United States, a few key laws aim to safeguard health from pollution and contaminants:

• The 1972 Clean Water Act is the country's main tool for controlling source water pollution, but the law is limited by enforcement issues and legal ambiguity over which bodies of water it governs.⁷⁴
• The 1974 Safe Drinking Water Act authorizes the US Environmental Protection Agency (EPA) to set national health-based standards for drinking water to protect against contaminants that are naturally occurring and/or caused by human activity. The SDWA focused primarily on treatment to provide safe drinking water. The 1996 amendments enhanced the law by recognizing source water protection, as well as funding for water system improvements and other components of safe drinking water, as important contributors to drinking water safety.⁷⁵
• US EPA’s 1991 Lead and Copper Rule requires systems to monitor drinking water at customer taps. If lead concentrations exceed an action level of 15 ppb or copper concentrations exceed an action level of 1.3 ppm in more than 10 percent of customer taps sampled, the system must undertake a number of additional actions to control corrosion and safeguard health.
• Further legislation and regulations are described on the EPA website: Regulatory Information by Topic: Water.

In the European Union, the Drinking Water Directive (Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption) is designed to protect human health from adverse effects of any contamination of water intended for human consumption by ensuring that it is wholesome and clean. 

A 2011 publication from the World Health Organization provides guidance on regulatory frameworks worldwide: Optimizing Regulatory Frameworks for Safe and Clean Drinking-water.