Water quality standards categorize water based on its intended use, distinguishing between water safe for consumption (potable) and water suitable only for non-ingestion purposes (non-potable). Showering with non-potable water presents a complex risk profile because contaminants can enter the body through multiple pathways, not just surface contact. Safety depends on what is accidentally swallowed or inhaled as a fine mist. Understanding these exposure routes and the specific contaminants involved is necessary to evaluate the true health risks.
Defining Non-Potable Water and Its Contaminants
Potable water is rigorously treated and tested to meet stringent health standards, making it safe for drinking, cooking, and personal hygiene. Non-potable water has not met these regulatory requirements and is unsafe for human consumption, though it may be used for irrigation or toilet flushing. This water often contains contaminants that fall into two main groups: microbial and chemical.
Microbial contaminants include pathogens such as bacteria, viruses, and protozoa that can cause gastrointestinal or respiratory diseases. Chemical contaminants range from heavy metals like lead, to volatile organic compounds (VOCs), and disinfection byproducts (DBPs) like trihalomethanes, which can be linked to long-term health issues. Non-potable water may also contain high concentrations of minerals or salts that cause skin irritation and lead to scale buildup. Regulatory standards, such as those set by the U.S. Environmental Protection Agency for drinking water, do not apply to non-potable sources, making contamination levels unpredictable.
Routes of Exposure During Showering
Showering involves three primary routes for contaminants to enter the body. The first is accidental ingestion, where small amounts of water are swallowed, introducing microbial pathogens or chemical toxins directly into the digestive system.
The second route is dermal absorption, where the skin absorbs chemicals during contact. Warm water causes blood vessels near the skin’s surface to dilate and pores to open, significantly increasing the skin’s permeability to contaminants like chlorine and heavy metals. For some volatile chemicals, dermal uptake during a shower can be comparable to or greater than the dose received from drinking the same water.
The most concerning route is the inhalation of aerosols, which are the tiny water droplets created by the showerhead. These respirable particles carry volatile chemicals, which vaporize easily in hot water, and airborne microbial pathogens deep into the lungs. This direct delivery bypasses the body’s natural filtering mechanisms, risking respiratory infections from bacteria like Legionella and Mycobacteria.
Specific Risks of Different Non-Potable Sources
The risk of non-potable water varies significantly depending on its origin, requiring a distinction between treated and untreated sources. Treated, or reclaimed, water is often derived from municipal wastewater that has undergone extensive processing for non-drinking uses, such as irrigation. Although treatment reduces the microbial load, reclaimed water may still contain residual pharmaceuticals, personal care products, and inorganic salts.
Untreated sources, such as raw private well water or roof-collected rainwater, carry the highest risks. Well water can be contaminated with naturally occurring contaminants like arsenic or human-caused pollutants such as nitrates and heavy metals. Rainwater can pick up microbial pathogens, bird droppings, and chemical residues from roofing materials, which may amplify in storage tanks.
The danger of untreated sources is compounded by a high microbial load, including pathogens like E. coli or Legionella that multiply rapidly in stagnant water. The lack of consistent testing and regulation for these private sources means the user is exposed to an unknown mix of chemical and biological agents.
Guidelines for Non-Potable Water Contact
Showering in non-potable water is risky due to inhalation and accidental ingestion. If using a source not verified as potable, it must be tested by a certified laboratory. Testing should check for microbial pathogens, especially total coliforms and E. coli, and relevant chemical contaminants like heavy metals.
If non-potable water must be used, minimize aerosol generation to reduce inhalation risk. This involves using a showerhead with a coarser spray pattern that produces larger droplets, or reducing the water temperature. Lower temperatures limit the volatilization of chemicals and the formation of fine mist. Running the water briefly before use also flushes out stagnant water that may harbor microbial growth.
Infants, young children, pregnant women, and immunocompromised individuals should strictly avoid exposure to non-potable water. These groups are disproportionately vulnerable to waterborne illnesses and the effects of contaminants like lead. Maintaining excellent ventilation in the shower area helps clear volatile chemicals or bioaerosols.