4.1 Drinking Water Sources & Quality

Introduction to Drinking Water Sources

Understanding the sources of our drinking water and the regulations ensuring its safety is fundamental for any Registered Environmental Health Specialist (REHS). Drinking water typically originates from two primary sources: groundwater and surface water. Each source has distinct physical, chemical, and biological characteristics that dictate the level of treatment required before it can be considered potable.

Groundwater vs. Surface Water Characteristics

Groundwater is located underground in aquifers, which are geological formations of porous rock, sand, or gravel. As water percolates through the soil, it undergoes a natural filtration process.

• Advantages of Groundwater: This natural filtration typically results in water with very low turbidity (cloudiness) and a significant reduction in microbiological pathogens (bacteria, viruses, and protozoa). Groundwater is also less susceptible to immediate contamination from surface spills or runoff. Its temperature remains relatively constant year-round.
• Disadvantages of Groundwater: Due to its prolonged contact with underground rock formations, groundwater often contains higher concentrations of dissolved minerals. It is frequently "hard" water, containing elevated levels of calcium and magnesium. It may also contain dissolved iron, manganese, and naturally occurring contaminants like arsenic or radon.

Surface Water includes rivers, lakes, streams, and reservoirs. It is open to the atmosphere and surface runoff.

• Characteristics of Surface Water: Surface water is highly vulnerable to contamination from agricultural runoff, industrial discharges, treated wastewater effluent, and natural organic matter. It typically has higher turbidity and a much higher microbial load, including pathogens like Giardia and Cryptosporidium. Surface water temperature fluctuates with the seasons and it generally contains fewer dissolved minerals (softer water) than groundwater. Because of its vulnerability, surface water requires comprehensive treatment, including filtration and disinfection, to meet potable water standards.

The EPA Safe Drinking Water Act (SDWA)

The Safe Drinking Water Act (SDWA) is the primary federal law in the United States that ensures the quality of Americans' drinking water. Under the SDWA, the Environmental Protection Agency (EPA) sets standards for drinking water quality and oversees the states, localities, and water suppliers who implement those standards.

Primary Drinking Water Standards

Primary standards are legally enforceable limits set by the EPA to protect public health by limiting the levels of specific contaminants that can adversely affect human health. These limits are known as Maximum Contaminant Levels (MCLs).

• Lead and Copper: Regulated under the Lead and Copper Rule (LCR). These metals primarily enter drinking water through the corrosion of plumbing materials. The action level for lead is 0.015 mg/L (15 ppb) and for copper is 1.3 mg/L. Exceeding these levels triggers mandatory water quality parameter monitoring, corrosion control treatment, and public education.
• Arsenic: A naturally occurring element that is highly toxic. The MCL for arsenic in drinking water is 0.010 mg/L (10 ppb). Long-term exposure is linked to various cancers and skin lesions.
• Nitrates: The MCL for nitrates is 10 mg/L (measured as Nitrogen). High nitrate levels are particularly dangerous to infants under six months of age. Nitrates convert to nitrites in the body, which bind to hemoglobin and inhibit oxygen transport in the blood, causing methemoglobinemia, commonly known as "blue baby syndrome."
• Coliforms: The Total Coliform Rule regulates microbiological quality. Total coliforms are used as indicator organisms. While most coliforms are harmless, their presence indicates that the water may be vulnerable to pathogens. The standard generally requires that no more than 5.0% of samples collected in a month can be positive for total coliforms.

Secondary Drinking Water Standards

Secondary standards are non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water. The EPA recommends secondary standards to water systems but does not require systems to comply.

• Taste, Odor, and Color: These affect the consumer's acceptance of the water.
• Iron and Manganese: While not a direct health hazard at typical levels, these can cause laundry and plumbing fixture staining (iron causes reddish-brown stains; manganese causes black stains) and impart a metallic taste. The secondary MCL for iron is 0.3 mg/L and for manganese is 0.05 mg/L.
• pH: The recommended pH range is 6.5 to 8.5. Water with a pH outside this range can be corrosive to pipes (releasing lead or copper) or cause scaling.

Waterborne Pathogens

Pathogens are disease-causing microorganisms. The primary concern in drinking water microbiology is the prevention of waterborne diseases transmitted through the fecal-oral route.

• Protozoa:
  • Giardia lamblia: Causes giardiasis. It forms environmentally resistant cysts that are highly tolerant to chlorine disinfection. Filtration is the most effective treatment.
  • Cryptosporidium parvum: Causes cryptosporidiosis. It forms oocysts that are extremely resistant to standard chlorine doses. Effective removal requires advanced filtration or alternative disinfection like UV light or ozone.
• Viruses: Enteric viruses (e.g., Norovirus, Hepatitis A, Rotavirus) are very small and can pass through some filters, but they are generally more susceptible to chlorine disinfection than protozoan cysts.
• Bacteria: Pathogenic bacteria include Vibrio cholerae (cholera), Salmonella typhi (typhoid fever), and Escherichia coli (E. coli, specifically pathogenic strains like O157:H7). Coliform bacteria (including generic E. coli) are used as indicators of potential fecal contamination.

Well Construction Standards

Proper well construction is critical to protecting groundwater sources from surface contamination. Environmental health specialists regularly inspect well installations to ensure compliance with sanitary codes.

• Sanitary Seal: A watertight seal at the top of the well casing is essential to prevent surface water, insects, and debris from entering the well.
• Casing Depth: The well casing must extend deep enough to prevent shallow, potentially contaminated groundwater from entering the well. The exact depth depends on local geology, but it generally must extend into an impervious layer or reach a significant depth below the water table.
• Grouting: The annular space (the gap between the well casing and the drilled borehole) must be filled with a sealing material, typically neat cement grout or bentonite clay. Grouting prevents surface water from channeling down the outside of the casing into the aquifer.
• Separation Distances: Wells must be located a safe distance from potential sources of contamination. While local codes vary, standard minimum separation distances include:
  • 50 to 100 feet from a septic tank or leach field.
  • 50 feet from a sewer line.
  • 100 feet from pastures or animal enclosures.