Water, known as the “universal solvent,” can dissolve a majority of substances compared to other liquids on earth. Because of this unique property, it is vulnerable to water pollution as toxic substances can easily dissolve and mix with water. When harmful substances such as chemicals or microorganisms get dissolved, it becomes contaminated, rendering it toxic to humans and the environment.
Water Pollution Sources
The United States Environmental Protection Agency (US EPA) identifies two broad categories of water pollution sources: point source pollution and nonpoint source pollution. Emissions from point sources in solid, liquid, and gas form and contaminants from nonpoint sources can go either into the ground or the surface water. An example of this is when airborne pollutants incorporate into rainwater affecting water quality, as seen in acid rain. The amount of water obtained from precipitation or irrigation improves the capability for these contaminants to reach surface water or groundwater.
Point Source Pollution
Section 502(14) of the Clean Water Act defines point source as an identifiable, confined, and distinct portage such as a ditch, pipe, channel, conduit, tunnel, well, rolling stock, concentrated animal feeding operation, container, or other floating vessel or crafts where toxic substances can be discharged.
In simpler terms, point source pertains to water sources that come from a single, confined, and identifiable channel. The EPA establishes limits on what a facility can discharge to a body of water in order to regulate point source pollution. An example of this is the Clean Water Act, which requires states to identify the total maximum daily load (TMDL) for each pollutant. This list is then submitted to the US EPA for approval.
Oils, solvents, fuel, and paint products are some of the most common groundwater point source pollutants. Even minimal quantities of these volatile organic compounds are enough to raise concerns on water contamination as it could potentially harm both aquatic life and human health. As an example, about four liters of trichloroethylene is enough to contaminate one billion liters of water.
Surface Water Contamination
Microorganisms such as Giardia, viruses, and bacteria are one of the most common point source pollutants of surface water. Moreover, high-temperature discharges, together with an increase of nutrients (e.g., phosphorus and nitrogen) foster excessive growth of plants. This leads to a subsequent decay of organic matter that can deplete oxygen levels which can harm aquatic life.
Nonpoint Source Pollution
Nonpoint source pollution, on the other hand, comes from many diffused sources and is usually caused by atmospheric deposition, land runoff, seepage, drainage, precipitation, or hydrologic modification. Any other sources of water pollution not listed and defined as ‘point source’ in Clean Water Act section 502(14) is regarded as a nonpoint source.
Runoff or water that has accumulated contaminants from gardens, parking lots, or construction sites and is emptied into rivers and streams is generally associated with nonpoint source pollution. Runoff in rural places can sweep sediment from the logged-over forest tracts and may also carry acid from flush pesticides, abandoned mines, and fertilizer from the farmlands. These washed off contaminants are likely to wind up in large bodies of water like lakes and rivers.
- Excess herbicides, insecticides, and fertilizers from residential areas and agricultural lands
- Acid drainage from abandoned mines and salt from irrigation practices
- Grease, oil, and toxic chemicals produced from energy production and urban runoff
- Eroding streambanks and sediment from construction sites, forest, and croplands
- Atmospheric deposition and hydromodification
- Bacteria and nutrients coming from pet washes, livestock, and damaged septic systems
Nonpoint source pollution is the leading cause of water pollution in the United States because it is challenging to regulate as there is no single, identifiable source. However, with the Clean Air Act and the Clean Water Act, laws have helped in limiting nonpoint source as well as point source pollution.