Water purification tablets are a portable chemical solution designed to make microbiologically unsafe water drinkable in survival or emergency situations. These small, lightweight tablets dissolve to release disinfecting agents that neutralize harmful microorganisms that cause waterborne diseases. They are a convenient method for disinfection when boiling water or using a filtration system is not possible. Their primary function is to kill pathogens, ensuring water is potable.
Chemical Mechanisms of Water Purification
Water purification tablets work by releasing a halogen-based chemical that acts as a powerful disinfectant to destroy pathogens. The most common active ingredients are chlorine-based compounds, such as sodium dichloroisocyanurate or chlorine dioxide, and historically, iodine. These compounds use an oxidation process to attack the cellular structure of microorganisms, disrupting the enzymes and proteins essential for survival and reproduction.
Chlorine dioxide is a potent oxidizer that effectively neutralizes bacteria and viruses. It is also capable of killing resistant protozoan cysts, like Giardia, and shows some efficacy against Cryptosporidium. Iodine functions similarly by binding to the nucleic acids and proteins of the microbes, inactivating them. However, iodine is less effective against protozoan cysts than chlorine dioxide. This chemical purification process focuses on killing microbes, which is distinct from filtration, which physically removes particles and sediment.
Step-by-Step Instructions for Use
Effective water treatment begins with clarifying the source water to ensure the chemical disinfectant can work efficiently. If the water is visibly cloudy or turbid, it must first be filtered through a clean cloth or coffee filter to remove large particulates and sediment. Removing physical impurities first allows the tablet’s active ingredient to focus on killing microbes, as disinfectants can be neutralized by organic debris.
After pre-filtering, the correct dosage must be determined by checking the manufacturer’s instructions, as the concentration and volume treated vary by product. Typically, one tablet is used to treat one quart or one liter of water. Drop the tablet into the measured volume of water, allowing it to fully dissolve while gently mixing the container. Briefly loosen the container cap and splash some treated water onto the threads to disinfect any pathogens clinging to that area.
A mandatory contact time is required for the chemical reaction to fully eliminate the microorganisms. For most modern tablets, this waiting period is a minimum of 30 minutes. Water temperature plays a role in efficacy, as colder water slows the chemical reaction. If the water temperature is below 59 degrees Fahrenheit, the contact time should be extended, potentially up to four hours, especially when targeting resistant protozoan cysts with chlorine dioxide.
Safety and Efficacy Considerations
While water purification tablets are effective at killing viruses, bacteria, and many protozoa, they have limitations regarding what they can remove. The chemical process does not address non-biological contaminants such as heavy metals, pesticides, industrial chemicals, or dissolved solids. If the water source is suspected of having chemical contamination, using a tablet alone is not sufficient to make the water safe.
A common drawback of chemical purification is the resulting taste and odor, often described as a chemical or medicinal aftertaste, particularly noticeable with iodine and traditional chlorine tablets. This taste can be mitigated by allowing the treated water to stand uncapped for a short period to allow the chemical odor to dissipate, or by using a secondary neutralizer tablet sometimes packaged with the purifier. Chlorine dioxide tablets are frequently preferred because they produce a less objectionable taste.
Health and Storage
For long-term or frequent use, health considerations are important, specifically concerning iodine-based products. Excessive or chronic iodine intake can be harmful to individuals with pre-existing thyroid conditions and is generally not recommended for pregnant women. To maintain their potency, tablets must be stored in a cool, dry place away from light and moisture. Efficacy decreases over time, so check the expiration date before depending on them in an emergency.