An approved source of potable water is any water supply that meets federal or state safety standards for human consumption. In the United States, the three main approved sources are public water systems regulated by the EPA, private wells that meet state and local construction and testing requirements, and bottled water regulated by the FDA. Each source follows a different path to approval, but all must deliver water free of harmful levels of bacteria, chemicals, and other contaminants.
Public Water Systems
Public water systems are the most common approved source of potable water in the U.S. A public water system is defined as any system that provides water through pipes or other constructed conveyances to at least 15 service connections, or serves an average of at least 25 people for at least 60 days per year. This includes municipal utilities, community wells serving subdivisions, and water supplies at schools or office parks.
These systems fall under the Safe Drinking Water Act, originally passed in 1974, which gives the EPA authority to set enforceable safety standards. The EPA currently regulates more than 90 contaminants across several categories: microorganisms like E. coli, Giardia, and Legionella; disinfection byproducts that form when chlorine interacts with organic matter; inorganic chemicals like lead, nitrates, and selenium; organic chemicals like benzene and atrazine; and radioactive particles. If your water comes from a public system, your utility is legally required to notify you whenever water quality falls below EPA standards.
Public systems draw their water from two broad sources: surface water (rivers, lakes, reservoirs) and groundwater (aquifers accessed through wells). Surface water systems go through more extensive treatment because the water is exposed to runoff, animal waste, and industrial discharge. Groundwater systems may need less treatment but still must meet the same contaminant limits.
Private Wells
About 23 million households in the U.S. rely on private wells, and these are handled very differently from public systems. Private wells are not regulated by the federal government under the Safe Drinking Water Act, and most states don’t regulate them either. That means the responsibility for ensuring the water is safe falls entirely on the well owner.
For a private well to be considered an approved potable source (for purposes like a home sale, a building permit, or a food service license), it typically needs to meet state or county requirements for well construction, placement, and water testing. Construction standards usually specify minimum distances from septic systems, fuel tanks, and livestock areas, along with proper casing depth and sealing to prevent surface water from seeping in. Testing requirements vary by jurisdiction but commonly include checks for coliform bacteria, nitrates, pH, and sometimes lead or arsenic depending on local geology.
Because no federal agency monitors private wells on an ongoing basis, annual testing is recommended. Contamination can develop over time as nearby land use changes, aging pipes corrode, or seasonal flooding introduces bacteria. A well that tested clean five years ago may not be clean today.
Bottled Water
Bottled water is regulated by the FDA rather than the EPA, since it’s classified as a packaged food product. The FDA requires bottled water companies to protect their sources from contamination, test the water, and follow good manufacturing practices during processing and bottling. FDA standards for bottled water generally mirror EPA standards for tap water, covering the same categories of contaminants at comparable limits.
Bottled water sources include springs, wells, and municipal supplies. If the source is municipal tap water, the label must indicate this unless the water has been sufficiently treated to qualify as “purified” or “distilled.” Spring water must come from an underground source that flows naturally to the surface. These distinctions affect labeling but not necessarily safety, since all bottled water must meet the same contaminant standards regardless of where it originates.
What Makes Water “Potable”
Potable simply means safe to drink. For water to earn that designation in a regulated context, it must fall within the limits set by the National Primary Drinking Water Regulations. These limits are expressed as Maximum Contaminant Levels (MCLs), the highest concentration of a given substance allowed in drinking water.
Some of the most closely watched contaminants and their current limits include:
- PFOA and PFOS (often called “forever chemicals”): 4.0 parts per trillion each, finalized in 2024. This is an extremely low threshold, reflecting growing concern about the health effects of long-term exposure to these industrial chemicals found in nonstick coatings, firefighting foam, and food packaging.
- Other PFAS compounds (PFHxS, PFNA, GenX chemicals): 10 parts per trillion each. When two or more of these appear together, the system must also meet a combined hazard index.
- Lead: No safe level exists, so the EPA uses an action level that triggers corrective steps. A 2024 rule now requires water systems nationwide to identify and replace all lead service lines within 10 years.
- Coliform bacteria: The presence of total coliforms signals possible contamination; the presence of E. coli specifically indicates fecal contamination and triggers immediate action.
- Nitrates: Particularly dangerous for infants, with a maximum of 10 milligrams per liter.
Water that exceeds any of these limits is not considered potable until the contamination is addressed through treatment, source replacement, or infrastructure repair.
Sources Used in Food Service and Construction
If you searched this question because of a food handler’s exam, building permit, or health inspection, the answer is usually straightforward: an approved potable water source is a connection to a regulated public water system, or a private well that has been tested and approved by your local health department. Health codes in most jurisdictions require food establishments to use water from one of these two sources. Hauled water or untreated surface water does not qualify.
For new construction, local building codes typically require either a public water connection or a permitted well with a passing water test before a certificate of occupancy is issued. The specific tests required and the agency that must approve results vary by county and state, so checking with your local health department is the most reliable way to confirm what qualifies in your area.