Filtered water, sourced from common household systems like refrigerator dispensers or pitcher filters, is generally safe and intended to improve water quality by reducing contaminants like chlorine, sediment, and certain heavy metals. These systems contribute to better taste and odor. However, the potential for illness from filtered water is real, although it almost always stems from system neglect. An improperly maintained filter can increase the risk of consuming harmful microbes or chemicals.
How Microbial Contamination Occurs
The primary component in most home filtration systems is activated carbon, which works by adsorption, drawing impurities into its highly porous structure. This large surface area is excellent for trapping organic compounds and chlorine, but it also creates a hospitable environment for microorganisms naturally present in tap water. When the filter is not replaced on time, the captured organic material begins to serve as a food source for bacteria, allowing them to multiply.
This process leads to the formation of a sticky, complex layer of microorganisms and their secretions, known as biofilm, within the filter media and housing. As the biofilm matures and the carbon becomes saturated, the microorganisms can “break through,” resulting in the release of water with a higher bacterial count than the original tap water. Furthermore, many filtration processes remove chlorine, the disinfectant that inhibits microbial growth, accelerating the potential for bacterial colonization.
Risks Beyond Biological Growth
Illness from filtered water is not solely limited to microbial contamination; chemical and material risks also exist, particularly with prolonged use. The plastic components of filter housings, pitchers, and internal parts are manufactured with various additives, such as plasticizers. Over time, and especially when water remains stagnant within the system, these chemicals can leach into the filtered water.
Compounds like Bisphenol A (BPA) or its common substitute, Bisphenol S (BPS), along with phthalates, are Non-Intentionally Added Substances (NIAS) that have been detected in water that has been in contact with plastic. These are known as endocrine-disrupting chemicals, which can potentially interfere with the body’s hormonal systems. Moreover, some aggressive filtration methods, such as reverse osmosis, can carry a non-acute health risk by excessively purifying the water. These systems can remove 92% to 99% of beneficial minerals like calcium and magnesium.
The World Health Organization has noted that drinking demineralized water may negatively impact the body’s homeostasis. While not causing acute illness, the long-term consumption of water stripped of these minerals may contribute to issues like mineral deficiencies and a slight increase in cardiovascular risk.
Safe Handling and Filter Maintenance
Preventing illness from a filtration system relies almost entirely on following the manufacturer’s maintenance instructions precisely. The most important action is adhering to the recommended filter replacement schedule, which is determined by either a time limit, often between two to six months, or a specific volume of water, typically measured in gallons. Ignoring these limits ensures that the activated carbon media becomes saturated, turning it into a microbial breeding ground.
Regularly cleaning the non-replaceable parts, such as the pitcher reservoir or external housing, is equally important to prevent biofilm formation. These components should be periodically washed with detergent and water or sanitized using a mild solution, like diluted bleach, following the instructions for the specific system. When installing a new cartridge, always flush or “prime” the filter with water for several minutes before use, as this removes any fine carbon particles and prepares the media for operation. If a system is left unused for an extended period, such as two weeks or more, it should be thoroughly sanitized and the water flushed out before consumption.