Tap water in developed nations is a complex solution, not simply pure H₂O. Sourced from rivers, lakes, and aquifers, it is treated by municipal systems before delivery. This process introduces naturally occurring minerals, intentionally added disinfectants, and trace environmental contaminants. The physiological effect of consuming this water is multifaceted, involving the foundational necessity of hydration and the subtle, long-term impact of its dissolved contents. Understanding tap water’s composition reveals how it contributes to essential bodily functions while introducing health considerations distinct from filtered or bottled water.
The Primary Role of Hydration
The primary function of tap water is providing the H₂O molecule necessary for life. The human body is approximately 60% water, and nearly all major systems depend on its continuous presence to function correctly.
Water serves as the body’s primary transport vehicle, carrying nutrients and oxygen to cells while simultaneously flushing out waste products. This function lessens the burden on the kidneys and liver, which rely on adequate fluid for efficient waste removal and urine formation. Water is also a medium for biochemical reactions and helps maintain the precise balance of dissolved substances, a state known as cellular homeostasis.
Water plays a significant role in mechanical and thermal regulation. It lubricates joints and acts as a shock absorber for organs and tissues, such as the brain and spinal cord. The high heat capacity of water buffers the body against extreme temperature variations, helping to regulate body temperature through perspiration.
Essential Minerals Delivered
Tap water naturally contains various inorganic compounds that contribute to its taste and offer minor nutritional benefits. The mineral content varies significantly based on the original water source, with groundwater often having higher concentrations than surface water.
Calcium and Magnesium are the most common beneficial minerals, often responsible for “hard water.” These elements contribute to bone health, muscle contraction, and nerve function. While the total contribution to the recommended daily intake is generally small, drinking water can provide a measurable percentage of these minerals, such as around 5% of the Daily Value for magnesium.
Fluoride is intentionally added to many municipal water supplies as a public health measure known as fluoridation. This practice is primarily aimed at improving dental health by strengthening tooth enamel and reducing tooth decay. The concentration is carefully controlled to provide dental benefits without exceeding levels that could cause dental fluorosis.
Health Effects of Water Treatment Byproducts
Water treatment facilities add chemicals to kill pathogens and prevent the spread of waterborne diseases like cholera and typhoid. The most common disinfectants used are chlorine and chloramines, which have been widely successful in safeguarding public health.
A side effect of this disinfection is the formation of compounds called Disinfection Byproducts (DBPs). These form when disinfectants react with naturally occurring organic matter in the source water. The most regulated DBPs are Trihalomethanes (THMs) and Haloacetic Acids (HAA5s).
Long-term consumption of water containing DBPs above regulatory limits has been associated with potential health risks. Studies have observed an association between exposure to chlorinated drinking water and an increased risk of bladder cancer. Trace amounts of these compounds may also pose risks to the liver, kidneys, and central nervous system over many years.
Potential Impact of Environmental Contaminants
Tap water can contain unwanted pollutants from environmental sources or aging infrastructure, in addition to treatment byproducts. These contaminants are not added for disinfection but rather enter the supply through runoff, industrial discharge, or corrosion.
Lead and Aging Infrastructure
Lead is a serious contaminant that typically enters drinking water from the corrosion of lead service lines, lead-containing brass fixtures, or lead solder in older plumbing systems. In the body, lead is a neurotoxin that can cause neurological damage, especially in children, hindering development and affecting cognitive function.
Per- and Polyfluoroalkyl Substances (PFAS)
PFAS, often called “forever chemicals,” enter the water supply from manufacturing sites and industrial waste. These synthetic chemicals accumulate in the body over time and have been linked to health issues such as thyroid dysfunction, liver damage, and certain types of cancer. A study estimated that at least 45% of the nation’s tap water contains one or more types of PFAS.
Other Environmental Pollutants
Other contaminants include arsenic, a naturally occurring element, or trace amounts of pesticides and herbicides found in source water due to agricultural runoff. Arsenic exposure is associated with an increased risk of skin, bladder, and lung cancers. Microplastics, tiny plastic fragments, are also pervasive in tap water and may cause tissue inflammation or endocrine disruption due to their physical presence and chemical additives.