The safety of underground water, known as groundwater, is complex and depends entirely on its specific location and geological environment. Groundwater is water that has seeped into the ground, filling the cracks and spaces within soil, sand, and rock formations below the water table. This water is stored in layers called aquifers, which serve as a significant source of drinking water for a large portion of the population. Safety is highly variable, ranging from pristine to heavily contaminated, meaning a cautious approach is always warranted for private sources.
Natural Filtration and Geological Risks
The Earth provides a natural purification system as water filters down through layers of soil and rock. Physical sieving strains out sediment and larger microorganisms. Chemical processes like adsorption bind dissolved contaminants to mineral grains, and microbial communities break down some organic pollutants.
Despite this natural filtration, geological formations can introduce inherent hazards into the water supply. Water that flows through specific types of bedrock can dissolve naturally occurring elements, leading to high concentrations of toxic substances. Arsenic, for instance, is a semi-metal that leaches from certain mineral deposits and poses a serious health risk, even in low doses. Radioactive elements like radon, a gaseous byproduct of uranium decay, can dissolve into groundwater, particularly in areas with granite rock formations.
High mineral content, often called hard water, is common but typically not a health hazard. Total dissolved solids (TDS), which include elements like calcium and magnesium, can affect the taste and cause scaling on plumbing and appliances. Elements like fluoride and iron can also occur naturally at high concentrations, requiring treatment before the water is suitable for consumption.
Anthropogenic Sources of Groundwater Pollution
Human activities introduce pollution that natural systems cannot always mitigate. Agricultural practices are a major contributor, primarily through the widespread use of fertilizers and pesticides. Excess nitrogen from fertilizers leaches into the ground, turning into nitrates in the groundwater, which are especially dangerous to infants.
Residential and commercial waste disposal also threatens groundwater quality. Septic systems, if improperly maintained or located too close to a well, can release pathogens, including bacteria and viruses, directly into the aquifer. Industrial operations contribute through the improper disposal of solvents, heavy metals, and volatile organic compounds (VOCs) that can seep deep into the subsurface.
Leaking underground storage tanks (USTs), often containing petroleum products, can contaminate large plumes of groundwater with harmful hydrocarbons. Landfills lacking adequate liners allow leachate—a liquid containing dissolved pollutants—to percolate down and mix with the underground water. These contaminants often require specialized testing to detect and advanced methods for removal.
Critical Steps for Testing and Monitoring
Private well owners are responsible for ensuring groundwater safety, as these systems are not monitored by public health agencies. Regular testing is the only way to accurately determine the water’s quality, since many contaminants are colorless and odorless. Experts recommend testing private well water at least once every year for a basic panel of common indicators.
The annual test should include several key indicators:
- Total coliform bacteria to check for potential fecal contamination.
- Nitrates, which indicate surface or septic system runoff.
- pH and Total Dissolved Solids (TDS) to measure water quality and potential corrosivity to plumbing.
Well owners should also contact their local health department to identify area-specific risks, such as high regional levels of arsenic, radon, or specific pesticides.
A more comprehensive screening, including heavy metals and volatile organic compounds, is prudent every three to five years. It is important to use a state-certified laboratory for testing to ensure the results are accurate and reliable. Well water should be tested immediately following any work on the well, after a flood, or if any noticeable change in the water’s taste, odor, or appearance occurs.
Effective Methods for Water Treatment
When testing reveals the presence of contaminants, specific treatment technologies are available to make the water safe for consumption. For bacterial contamination, common in private wells, ultraviolet (UV) light disinfection neutralizes microorganisms without using chemicals. Another option is chemical shock chlorination, which is typically used as an initial treatment to disinfect the entire well and plumbing system.
Chemical and mineral contaminants require technologies designed to remove dissolved solids. Reverse osmosis (RO) systems, often used at the point-of-use (e.g., kitchen sink), use a semi-permeable membrane to remove up to 99% of nitrates, heavy metals, and fluoride. For removing organic chemicals like solvents and pesticides, activated carbon filtration is highly effective as the pollutants adsorb onto the surface of the carbon granules.
For high levels of mineral content causing hard water, ion exchange systems (water softeners) remove calcium and magnesium. Point-of-entry systems treat all the water entering the home, while point-of-use systems treat water only at a single tap, offering a targeted solution for drinking and cooking water. The selection of the appropriate treatment system should always be based on the specific contaminants identified in the water quality test.