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Chlorine and Iodine water purifying tablets expire after 3 to 5 years and silver-based water purifying tablets expire after 10 years. All water purifying tablets expire within 1 year after initial opening or if the recommended storage conditions are not met. Water purification tablets are an effective way to clean and sterilize water and are essential when traveling or to have as a backup around the home. However, knowing if and when water purifying tablets expire can be difficult especially as it can vary between brands, chemical ingredients, storage conditions and even the packaging type. Everyone needs to know exactly when their water purification tablets will expire. So, to save you a lot of time and energy, I’ve put together a ton of information on when and why different water purification tablets expire. I'll also explain how to tell if they have gone bad, where the expiry dates are located (and how to interpret them), and what effect packaging, storage conditions and opening them up has on their expected shelf life. When water purification tablets expire There are many different brands of water purifying tablets, each with their own expiry. Here is the expiry (in years) for the top brands of water purification tablets: Aquatabs 1000 Tablets: 3 years Aquatabs Food-Safe Tablets: 3 years Aquatabs Multipurpose Tablets: 3 years Katadyn Micropur MP1 Tablets: 4 years Potable Aqua Chlorine Dioxide Water Purification Tablets: 4 years Oasis Water Purification tablets: 5 years Aquamira Water Purifier Tablets: 5 years Aquatabs Sterinova Tablet: 5 years Aquatabs Water Purification Tablets: 5 years Katadyn Micropur Classic MC 1T Tablets: 10 years Coghlan's Emergency Drinking Water Germicidal Tablets: Expiry not required Coleman water purification tablets: Expiry not required Potable Aqua Drinking Water Germicidal Tablets: Expiry not required Potable Aqua with PA+ Drinking water Germicidal Tablets: Expiry not required The brands listed above are in no particular order of which one is better or worse, instead they are in order of how long they last according to the manufacturer. The manufacturers expiry date is determined by the chemical stability of what’s in the tablet. Water purification tablets are a combination of active ingredients (sterilizers) and non-active ingredients. On the ingredients list, the non-active ingredients are called “Other ingredients” and usually make up the bulk of each tablet. They not only provide tablet bulk, but can also help with solubility, stability and preservation over the tablets expected shelf life. The active ingredients in water purifying tablets make up a much smaller percentage of the tablet compared to the non-active ingredients but they are responsible for all of the sterilization work. Active ingredients are typically chlorine based or iodine based; however, silver based or mineral-salt (liquid) based forms also exist. Expiry of chlorine water purification tablets Chlorine-based tablets will expire between 3 and 5 years. The main difference here is what type of container they come in and if they are individually sealed. Chlorine water purifying tablets that come individually sealed last between 4 and 5 years. Chlorine water purifying tablets that come in a plastic tub only last around 3 years. So, if you are buying chlorine water purifying tablets and want them to last a long time, you’re already a few years ahead if you buy ones that come individually sealed. Here is a table of the chlorine-based water purification tablets, their expiry, and what container types they come in: BrandExpiryContainer TypeAquatabs 1000 Tablets3 yearsPlastic tubAquatabs Food-Safe Tablets3 yearsPlastic tub Aquatabs Multipurpose Tablets3 yearsPlastic tub Katadyn Micropur MP1 Tablets4 yearsIndividually sealed tabletsPotable Aqua Chlorine Dioxide Water Purification Tablets4 yearsIndividually sealed tablets Oasis Water Purification Tablets5 yearsIndividually sealed tablets Aquamira Water Purifier Tablets5 yearsIndividually sealed tablets Aquatabs Sterinova Tablets5 years Individually sealed tablets Aquatabs Water Purification Tablets5 YearsIndividually sealed tablets Notice that granule and powder forms tend not to last as long as liquids. BrandExpiryContainer TypeFormAquatabs granules 2 yearsPlastic tub GranuleProcter & Gamble’s (P&G) Day One Response Purifier Of Water 3 years Individual sachets PowderChlor-Floc US Military Water Purification Powder (AKA GI issue water purification) 3 years Individual sachets PowderAquamira Chlorine Dioxide drops 4 yearsPlastic bottle LiquidPurogene Drinking Water Treatment and Water System Sanitizer 5 yearsPlastic bottle Liquid Expiry of silver water purification tablets Silver-based water purifying tablets have one of the longest expiry dates. I've personally used silver water purifying tablets in Nepal (up Mt. Everest), and throughout Asia and have never had a problem. Katadyn make two water purifying products that use silver sterilization: Katadyn Micropur Classic MC Tablets, and Katadyn Micropur Classic MC Liquid The tablet form expires after a whopping 10 years and each tablet comes individually wrapped. The Liquid form has about half the shelf life (5 years) of the tablets. Water Purification Guide has more information about how silver can purify water available here. Expiry of iodine water purification tablets According to the EPA, iodine water purification tablets are not required to have an expiry date printed on the packaging. This is because the EPA considers water purification tablets PESTICIDES and under the US Code of Federal Regulations (CFR): “Pesticides aren’t required to have labelled expiration dates unless it is determined that the formulation significantly changes chemical composition… over a one-year storage stability study” (ref 1) Basically, this means that if the ingredients in ANY water purifying tablet can remain relatively stable over 1 year, then it doesn’t require an expiry date printed on the packet. This is why you can never find an expiry date on iodine water purifying tablets! Nice! So, do iodine water purification tablets ever expire? Iodine tablets will break down over time just like the other types of water purifying tablets. Despite, iodine tablets not requiring an expiry date, most companies still suggest their products will in fact expire after 4 YEARS even if they are unopened and maintained under their recommended storage conditions. This is just not made very clear on the packaging (or on their websites)! The iodine water purification tablets below don't print an expiry date on their packaging, but do have a printed lot number code (manufacture number). If you want to learn how to decipher these lot number codes to get the expiry date then keep reading. BrandExpirySuggested ExpiryPotable Aqua Drinking Water Germicidal TabletsNot required 4 yearsPotable Aqua with PA+ Drinking Water Germicidal TabletsNot required4 yearsCoghlan's Emergency Drinking Water Germicidal TabletsNot required4 yearsColeman's Water Purification TabletsNot required4 years Can you use water purification tablets past their expiry? It’s best to not use any water purification tablet past its expiry date as the stability and chemical composition of the tablets may have changed and may be ineffective at killing microbes. Using water purification tablets past their expiry may also be harmful to you. Water purification tablets are quite cheap, so keeping an in-date supply ready for when you need them is simply a safer and better way to go. How long do water purifying tablets last once they are opened? If the product has been opened, or the recommended storage conditions have not been met, water purification tablet manufacturers suggest the products shelf life reduces to just 1 year. This 1 year shelf life also goes for iodine-based tablets. Here are the general storage guidelines for ALL types of water purifying tablets: Store in dry conditions Store in cool and controlled temperatures Keep out of direct sunlight Remember, the storage directions may vary slightly between brands so read over the packaging before you store them away. If you have an opened container of water purifying tablets that are not individually wrapped, you may be wondering if they can go bad. Here's how you can check if they have started to degrade: Gently squeeze one tablet between your fingers. If it crumbles easily then they have started to degrade and are probably no good. For iodine-based tablets, discoloration is a dead giveaway that they have started to degrade. If the tablets are yellowish/green in color then they have gone bad, but if they are still grayish/brown then they are good to go. It’s always a good idea to check for any tablet color change before use. Additional checks for iodine tablets include making sure there is still good lid closure and the wax seal is intact. Also, check to see if the metal cap shows no signs of physical deterioration (i.e. no rusting). You can continue to use the iodine tablets for quite some time after opening if you do the checks listed above and store them well. One exception to this rule is the brand Polar Pure. Polar Pure is not an iodine tablet, but instead uses crystalline iodine to purify water. If stored correctly, an opened bottle of Polar Pure should continue to be usable indefinitely, or at least until the crystalline iodine runs out. Where can I find the water purifying tablets expiry date? The location of the expiry date can vary between water purification products. Chlorine-based and silver-based water purification tablets are required to print the expiry date on the actual box, plastic tub, or sometimes, on the foil of the individually wrapped tablets. As discussed above, iodine-based water purification products are not required to print an expiry date anywhere on the packaging. Instead they typically print a five- or six-digit number, which looks suspiciously like an expiry date, called a lot number code. You can use this lot number code to work out when the product was MANUFACTURED and then work forwards to calculate when you might consider them EXPIRED and look at getting a replacement. Here’s how you can decipher the lot number code on iodine water purification tablets: Example lot number code: 1 19 156. The first digit(s) refers to the MONTH of manufacture The second and third digits combined refer to the YEAR of manufacture Any digits beyond the YEAR digits refers to the BATCH NUMBER So, in the example above, the product was manufactured in the 1st month of 2019 and was the 156th batch or product made. Keep in mind that even though iodine water purification tablets don’t require an expiry date, most manufacturers, still suggest a shelf life of around 4 years for unopened containers and 1 year for opened containers. Therefore, based on an expiry date of 4 years, this example lot number would indicate you should think about getting a replacement around the 1st month in 2023. Related questions What water purification tablets does the military use? The US military use Chlor-Floc US Military Water Purification Powder, which is also known as GI issue water purification tablets and has an expiry date of 3 years. It’s active ingredient (disinfectant) is sodium dichloroisocyanurate and comes with a flocculant and coagulant to purify the worst water under any conditions. What is the shelf life of water treatment drops? The shelf life of liquid forms of water treatment drops include: Aquamira Chlorine Dioxide drops: 4 years Katadyn Micropur Classic MC Liquid: 5 years Purogene Drinking Water Treatment and Water System Sanitizer: 5 years Purinize Drops: Unlimited Reference: https://www.epa.gov/pesticide-labels/pesticide-labeling-questions-answers

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