Source water is the untreated water drawn from natural bodies—such as rivers, lakes, reservoirs, and underground aquifers—before it undergoes purification for a community’s public drinking water system. The quality of this raw water directly influences the complexity and expense of the treatment required to make it safe for consumption. Therefore, protecting source water is a public health measure essential for ensuring the safety and reliability of the finished drinking supply.
The Two Primary Categories of Source Water
Source water is broadly categorized into two types based on location: surface water and groundwater. Surface water includes all bodies exposed to the atmosphere, such as rivers, streams, lakes, and reservoirs. Because it is open to the environment, surface water is generally more accessible for large municipal systems.
The disadvantage of surface water is its high susceptibility to contamination from environmental factors and human activity, often experiencing rapid quality changes after storm events. Exposure to runoff means it often contains higher levels of sediment, biological contaminants like bacteria and viruses, and fluctuating chemical concentrations. Consequently, surface water requires extensive filtration and disinfection at the treatment plant to meet safety standards.
Groundwater is water stored beneath the Earth’s surface in porous rock and soil formations known as aquifers. It originates from rain and snowmelt that slowly percolates downward through layers of soil and rock, which acts as a natural filtration process. This natural purification results in water that is less susceptible to microbiological contamination and sudden quality changes compared to surface water.
Groundwater is not immune to contamination and presents unique challenges. As it moves through rock layers, it tends to dissolve minerals, sometimes leading to naturally high concentrations of compounds like calcium, iron, or toxic elements. Once an aquifer becomes polluted, the slow movement of the water means the contamination is persistent, making cleanup efforts extremely difficult and costly.
Factors That Compromise Source Water Quality
Contamination of source water arises from two main categories: point source and non-point source pollution. Point source pollution is identifiable, originating from a single, specific location, such as a discharge pipe from an industrial facility or a municipal wastewater treatment plant outfall. These sources often introduce heavy metals, solvents, or polycyclic aromatic hydrocarbons (PAHs) directly into surface waters.
Wastewater treatment plants, even when operating correctly, can release trace amounts of pharmaceuticals, personal care products, and nutrients like nitrogen and phosphorus. Agricultural point sources, such as concentrated animal feeding operations (CAFOs), also discharge waste high in nutrients and bacteria from their lagoons.
Non-point source pollution is more difficult to manage because it comes from diffuse areas across a landscape, carried by rainfall or snowmelt runoff. Agricultural runoff is a major contributor, washing fertilizers, pesticides, and herbicides from farm fields into streams and groundwater. Urban stormwater runoff carries contaminants from paved surfaces, including oil, grease, road salts, pet waste, and sediment.
Natural geological formations can also compromise source water quality, particularly in groundwater. Certain regions have bedrock containing naturally occurring elements like uranium, which decays into radioactive radon gas. Arsenic is another natural contaminant, released into groundwater as water interacts with arsenic-bearing minerals. Chronic exposure to these elements is linked to serious health outcomes, including various forms of cancer and kidney toxicity.
Strategies for Source Water Protection
Protecting source water involves preventing contamination before it reaches the intake point or wellhead. This begins with creating watershed management plans, which delineate the area contributing water to the source and inventory potential contaminant sources. This assessment is then used to develop targeted actions to mitigate risks.
Land use controls are implemented through local ordinances and zoning to limit activities near water sources. For surface water, this involves establishing protective buffer zones along shorelines where development is restricted to filter runoff. For groundwater, wellhead protection areas are established, often prohibiting high-risk activities like new sanitary landfills or hazardous material storage facilities near the well.
Regular monitoring programs track contaminants and evaluate the effectiveness of protection efforts, allowing utilities to detect changes and respond quickly to pollution events. Public education initiatives also inform residents and businesses about pollution prevention, such as responsible use of lawn chemicals and proper septic system maintenance.
The federal Safe Drinking Water Act (SDWA) requires states to assess the susceptibility of their public water systems to contamination. The SDWA encourages a “multi-barrier approach” that recognizes source water protection as the first line of defense, reducing the need for costly and complex treatment later.