If you're concerned about the environment and water quality, you may wonder what kind of things pollute the water around you. According to the U.S. Environmental Protection Agency and the National Institutes of Health, the top three water pollutants are "soil, nutrients and bacteria." It's important to understand how these and other common pollutants get into the water supply.
Bacteria and Parasites from Sewage
If sewage is improperly treated, it can contaminate water with a variety of bacteria and other parasites. Contaminants from sewage include cryptosporidium, salmonella, giardia and parasitic worms. This kind of contamination is more commonly a problem in less-developed countries but can happen in developed countries, causing illness in those who drink the contaminated water. For instance, thousands of residents of a community in Georgia became ill from a cryptosporidium contamination of the water supply in 1987.
Manufacturing plants are supposed to treat wastewater before discharging it into the surrounding water, but some industrial waste can still make it into the water supply. Common industrial contaminants include sulfur dioxide and other acids, heavy metals and industrial solvents. Iron and steel production and mining operations can also pollute water with ammonia, cyanide and arsenic.
Fertilizer and Lawn Chemicals
Fertilizers and pesticides from agricultural lands and chemicals used on lawns in residential areas contaminate the groundwater and nearby lakes and rivers. When rain washes over farms or yards treated with these chemicals, pesticides and nutrients from the fertilizers flow into the water supply. When a body of water becomes too enriched with certain nutrients from manure and fertilizer, it encourages algae blooms. These blooms block sunlight from underwater plants, reducing the oxygen in the lake water and threatening wildlife that live in or near the body of water.
Silt and Soil
Lakes and other bodies of water naturally undergo changes as rivers and rainstorms wash silt and soil into them. However, humans can speed up the process through agricultural practices and through urban development that erodes the banks of rivers and lakes. As the silt and soil build up in the lake, they encourage new kinds of plant and animal populations to grow and others to decrease. The process often robs the body of water of oxygen that living things need. As silt and soil are deposited, the bottom of the body of water is built up and the lake or pond gradually becomes shallower, adding to the change in the aquatic ecosystem.
Though wastewater is treated before being discharged, small amounts of detergents still end up in the water supply, contaminating it with phosphates. Phosphates from detergents, like nutrients from fertilizers, contribute to the growth of algae. This can affect the oxygen levels in bodies of water and harm plant and animals living in the body of water. Today, many detergents low in phosphates are available for purchase.
Gasoline, oil and other petrochemicals also contribute to water pollution. This can occur on a large scale when an oil tanker springs a leak, as in the Exxon Valdez tanker spill off the coast of Alaska in 1989. On a smaller scale, water pollution occurs when the motor on a boat leaks into a lake or when rain washes oil drips from a driveway into groundwater. Maintaining vehicles and catching and repairing drips and leaks early can minimize this kind of pollution.