Chlorine is added to tap water for disinfection, a process foundational to modern public health that prevents waterborne diseases. Many people question whether this protective measure poses a risk. Understanding the effects of drinking chlorinated water requires separating the immediate, regulated presence of chlorine from the potential long-term concerns related to the chemical byproducts it creates.
Why Chlorine Is Added to Drinking Water
Chlorine is introduced into public water supplies to kill harmful microorganisms that cause disease. This practice dates back to the early 1900s and is regarded as a significant public health advancement, virtually eliminating widespread outbreaks of diseases like cholera and typhoid fever. Chlorine is effective because it is a powerful oxidant that destroys bacteria, viruses, and protozoa.
A major advantage of using chlorine is that it leaves a residual disinfectant in the water as it travels through the distribution system. This residual prevents recontamination that might occur through leaks or pipe breakages. The amount of chlorine added is regulated by agencies like the Environmental Protection Agency (EPA), which sets a Maximum Residual Disinfectant Level (MRDL) of 4.0 milligrams per liter (mg/L) for drinking water.
Immediate Effects of Drinking Chlorinated Water
The direct consumption of standard chlorinated tap water causes no adverse health effects for the majority of people. The small amounts of chlorine used for disinfection are considered safe for human consumption. The most common and noticeable immediate effects relate to the sensory experience of the water.
Many individuals detect a distinct, sometimes unpleasant, chemical or “bleach-like” taste and odor due to the residual chlorine. At regulated levels, acute toxicity is not a concern. However, consuming water with exceptionally high chlorine levels, far exceeding public standards, could lead to mild digestive tract irritation, such as nausea or stomach discomfort. Contact with chlorinated water can occasionally cause dryness or irritation for people with sensitive skin, though this is usually related to bathing rather than ingestion.
Understanding Disinfection Byproducts and Long-Term Concerns
The primary concern regarding chlorinated water is not the chlorine itself but the chemical compounds it creates when reacting with natural organic matter in the source water. Disinfection Byproducts (DBPs) form when chlorine interacts with decaying vegetation, sediment, and other organic material. Two commonly monitored groups of DBPs are Trihalomethanes (THMs), such as chloroform, and Haloacetic Acids (HAAs).
Chronic, long-term exposure to elevated levels of DBPs has been associated with potential health risks. Studies suggest a link between prolonged, high-level DBP exposure and an increased risk of certain cancers, specifically bladder and colorectal cancer. Reproductive and developmental concerns have also been raised, indicating a connection between high THM exposure during pregnancy and adverse birth outcomes.
The EPA regulates DBP concentration, setting Maximum Contaminant Levels (MCLs) for Total Trihalomethanes (TTHMs) at 80 micrograms per liter (\(\mu\)g/L) and for five specific Haloacetic Acids (HAA5) at 60 \(\mu\)g/L. These regulations balance the necessity of disinfection to prevent immediate illness with the need to limit long-term exposure. DBP formation is influenced by factors like the amount of organic matter, water temperature, and the contact time between the chlorine and the organic material.
Methods for Reducing Chlorine and Byproducts
Individuals concerned about the taste, odor, or long-term effects of chlorine and its byproducts have several options to reduce exposure. The simplest method for reducing the residual chlorine taste is allowing the water to sit in an open container for a few hours, permitting the volatile chlorine to dissipate through evaporation. Boiling water can also accelerate chlorine evaporation, though this is practical only for small quantities.
For more comprehensive removal, filtration systems are effective. Activated carbon filters, found in pitcher filters, faucet mounts, and whole-house systems, work by adsorbing chlorine and many DBPs onto the carbon material surface. Reverse osmosis systems can remove chlorine, chloramines, and a wide range of other contaminants by forcing water through a semipermeable membrane. Using a high-quality filter that targets both chlorine and Disinfection Byproducts is a practical way to improve the sensory quality of the water while mitigating chronic exposure risks.