Water & Adults

Every time you wash your hands, take a shower, or soak in the tub, water comes into direct contact with your skin — the body's largest organ and its primary physical barrier against the outside environment. The composition of that water can influence how your skin feels, how effectively you clean, and how your skin responds over time.

Mineral and Soap Interaction

Water that contains higher concentrations of dissolved calcium and magnesium — commonly referred to as "hard water" — reacts with the fatty acids in soap to form what chemists call soap scum (calcium or magnesium stearate). This insoluble residue does not rinse away easily and can leave a film on the skin surface.

• Reduced lathering: Hard water requires more soap or detergent to produce the same lather as soft water. This often leads people to use more product, which can contribute to skin dryness.
• Residue on skin: The soap-mineral film left behind can clog pores and trap bacteria, potentially contributing to irritation in people with sensitive skin.
• pH considerations: Healthy skin maintains a slightly acidic surface pH (around 4.5 to 5.5), often called the acid mantle. Water with a notably high or low pH can temporarily shift the skin's surface chemistry, although the skin typically restores its natural pH within a few hours.

Skin Barrier Science

The outermost layer of your skin, the stratum corneum, functions like a brick-and-mortar wall. Skin cells (corneocytes) are the "bricks," and lipids — ceramides, cholesterol, and fatty acids — act as the "mortar." This barrier keeps moisture in and irritants out. Prolonged or frequent exposure to water, especially hot water, can strip away some of these natural lipids, temporarily weakening the barrier and increasing transepidermal water loss (TEWL). People who wash their hands frequently or take long, hot showers may notice drier skin as a result.

Chlorine and Skin Dryness

Municipal water supplies typically use chlorine or chloramine as a disinfectant to control microbial growth in the distribution system. While these disinfectants are effective at making water microbiologically safe, they are oxidizing agents by nature.

• Chlorine can react with the natural oils on the skin surface, breaking down lipids and potentially accelerating moisture loss.
• At the concentrations typically found in tap water (0.2 to 4.0 mg/L for free chlorine), most adults do not experience significant irritation. However, individuals with eczema, psoriasis, or generally sensitive skin may notice that chlorinated water exacerbates dryness or itching.
• The sensation of "tight" or "squeaky-clean" skin after showering in chlorinated water is partly due to the removal of natural oils and partly due to the interaction between chlorine and skin proteins.

Showering is one of the most common daily exposures to household water, and it involves more than just skin contact. Hot showers produce steam, and that steam can carry dissolved or volatile substances from the water into the air you breathe in an enclosed bathroom.

Steam Inhalation

When water is heated and aerosolized through a showerhead, it creates fine droplets and water vapor. This process can release certain dissolved gases and volatile compounds from the water into the bathroom air. In a small, enclosed bathroom with limited ventilation, concentrations of these airborne substances can build up during the course of a shower.

• Chlorine and chloramine off-gassing: Both chlorine and chloramine can volatilize from hot water. Chlorine is more volatile of the two, meaning it escapes into the air more readily. This is why some people notice a stronger chlorine smell in a steamy bathroom than when drinking the same water cold.
• Inhalation pathway: The lungs have a very large surface area and a thin membrane designed for gas exchange. Some researchers have noted that inhalation exposure during showering can be a meaningful route of contact with volatile water contaminants — in some cases contributing as much or more total body exposure as drinking the water itself.
• Practical consideration: Running bathroom ventilation fans or leaving a door slightly open during showers helps disperse steam and reduce the concentration of any volatilized compounds.

Volatile Compounds

Beyond chlorine, other volatile organic compounds (VOCs) may be present in some water supplies depending on the source and local conditions. Trihalomethanes (THMs) — a class of disinfection byproducts formed when chlorine reacts with naturally occurring organic matter in the water — are among the most studied. THMs are volatile, meaning they can become airborne when water is heated or agitated.

• The EPA regulates total trihalomethanes (TTHMs) in public water systems at a maximum of 80 parts per billion (ppb) as an annual average.
• Concentrations can vary seasonally — warmer months often produce higher THM levels because source water contains more organic matter and chlorine reacts more readily at higher temperatures.
• Hot showers and baths tend to release more THMs into the air than cold water use, simply because volatilization increases with temperature.

Hair is primarily composed of a protein called keratin, arranged in overlapping cuticle layers that protect the inner cortex. The minerals and chemicals in your water supply can interact with this protein structure in ways that affect how hair looks, feels, and behaves over time.

Mineral Binding

Calcium and magnesium ions in hard water carry a positive charge, and they are attracted to the negatively charged surface of hair fibers. This electrostatic attraction causes mineral ions to bind directly to the hair shaft, particularly to damaged areas where the cuticle is lifted or broken.

• Calcium deposits: Calcium binds readily to hair proteins and can form a crystalline coating on the hair shaft over time. This coating can make hair feel stiff, rough, or "crunchy" and can interfere with the absorption of conditioners and styling products.
• Color-treated hair: Mineral deposits may cause color-treated hair to fade more quickly or develop unwanted tonal shifts. Blonde hair, for example, can develop a brassy or greenish tint from copper or iron mineral deposits.
• Iron and manganese: Even at low concentrations, dissolved iron and manganese can deposit on hair, sometimes causing a reddish-brown or darkened discoloration, particularly on lighter hair.

Buildup Mechanisms

Mineral buildup is cumulative. Each wash adds a thin layer of mineral deposits, and because these deposits are not fully soluble in water, they are not completely removed by normal shampooing.

• Reduced porosity: As mineral layers accumulate, hair can become less porous, making it harder for moisture and conditioning treatments to penetrate the hair shaft.
• Increased friction: A mineral-coated cuticle creates more friction between individual hair strands, which can increase tangling and make hair more difficult to manage.
• Scalp considerations: The same mineral residues that affect hair can also build up on the scalp. Combined with soap scum from hard water, this buildup may contribute to flakiness, itching, or a feeling of heaviness at the roots.
• Clarifying treatments: Chelating shampoos (formulated with ingredients like EDTA or citric acid) are designed to bind to mineral deposits and remove them from the hair shaft. Some people in hard water areas use these periodically to manage mineral buildup.

Water is not truly "tasteless." The minerals, dissolved gases, and treatment chemicals present in any water supply give it a characteristic flavor profile. Human taste perception is remarkably sensitive to certain substances, and individual variation in taste sensitivity means the same glass of water can taste very different from one person to the next.

Chlorine Taste Thresholds

Chlorine has both a taste and an odor that many people can detect at low concentrations. Research suggests that the average person can detect chlorine in water at concentrations as low as 0.3 to 0.5 mg/L, though some individuals are sensitive to levels below 0.2 mg/L.

• Chloramine difference: Chloramine (a combination of chlorine and ammonia used by some utilities for longer-lasting disinfection) tends to produce a less noticeable taste and odor than free chlorine, although some people describe it as a mild "flat" or "chemical" taste.
• Temperature effect: Cold water generally suppresses taste perception. The same water may taste more noticeably of chlorine when served at room temperature than when chilled.
• Letting water stand: Because chlorine is volatile, leaving a glass of water uncovered for 20 to 30 minutes allows some free chlorine to off-gas, which can reduce the noticeable taste. Chloramine, however, is more stable and does not dissipate as readily.

Metallic Taste

A metallic taste in tap water is a common complaint and can stem from several sources:

• Iron and manganese: These naturally occurring metals are among the most common causes of metallic-tasting water. They can enter the water supply from geological sources or from corroding iron pipes in the distribution system or household plumbing.
• Zinc and copper: Brass fittings and copper plumbing can leach small amounts of these metals into water, especially when water sits in pipes for extended periods (overnight, for example). Running the tap for 30 to 60 seconds before drinking can help flush stagnant water.
• Low pH: Water with a lower pH (more acidic) is more likely to dissolve metals from pipes and fixtures, which can contribute to a metallic taste.
• Total dissolved solids (TDS): The overall mineral content of water shapes its taste profile. Very low TDS water can taste "flat" or "empty," while higher TDS levels contribute body, sweetness, or minerality. Most people find water in the 100 to 300 mg/L TDS range pleasant to drink.

Conversations about water quality often focus on acute risks — is this water safe to drink right now? But researchers also study what happens when people are exposed to low levels of certain substances over many years. This field, known as chronic exposure assessment, is an active area of scientific inquiry with evolving findings.

PFAS Research

Per- and polyfluoroalkyl substances (PFAS) are a large family of synthetic chemicals that have been manufactured and used in a variety of industries since the 1940s. Sometimes called "forever chemicals" because of their strong carbon-fluorine bonds, PFAS resist degradation in the environment and can persist in water supplies.

• What we know: Epidemiological studies have associated certain PFAS compounds (particularly PFOA and PFOS) with a range of health outcomes in populations with high occupational or environmental exposure. These associations are being studied further to better understand dose-response relationships.
• Regulatory landscape: The EPA established enforceable maximum contaminant levels (MCLs) for several individual PFAS compounds in drinking water in 2024, reflecting growing scientific understanding. State-level regulations vary and in some cases are more stringent than federal standards.
• Balanced perspective: The presence of PFAS in a water supply does not automatically mean harm. Concentration levels, specific PFAS compounds, duration of exposure, and individual factors all matter. Testing is the most practical step for understanding your own situation.

Disinfection Byproducts

When chlorine or other disinfectants react with naturally occurring organic matter (such as decaying leaves or algae) in source water, they can form disinfection byproducts (DBPs). The most commonly measured DBPs include trihalomethanes (THMs) and haloacetic acids (HAAs).

• The EPA regulates total trihalomethanes at 80 ppb and five haloacetic acids (HAA5) at 60 ppb as annual running averages in public water systems.
• Some long-term epidemiological studies have explored associations between DBP exposure and certain health outcomes. This research is ongoing and results are interpreted within the broader context of multiple contributing factors.
• It is important to note that disinfection itself is one of the greatest public health achievements in water treatment history. The goal of DBP regulation is to minimize byproduct formation while maintaining effective disinfection — a balancing act that water utilities manage continuously.

What Chronic Exposure Means

Chronic exposure refers to repeated contact with a substance over a long period — typically years or decades. In the context of drinking water, this accounts for the fact that most people drink, cook with, and bathe in their tap water every day for the duration of their time living in a particular location.

• How standards are set: Regulatory agencies like the EPA set maximum contaminant levels by estimating a concentration at which a person could consume the water daily over a lifetime (typically modeled as 70 years) with an adequate margin of safety. These standards incorporate uncertainty factors to account for gaps in scientific knowledge.
• Individual variability: Age, body weight, overall health, genetics, and other environmental exposures all influence how an individual responds to any given substance. Regulatory limits are designed to be protective for the general population, including sensitive subgroups.
• The role of awareness: Understanding what is in your water is a practical first step. Annual water quality reports (Consumer Confidence Reports) from your utility, independent laboratory testing, and credible public databases can all provide useful information about your local water supply.