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Most water purification tablets do expire. Of the two most common types, Aquatab tablets expire after five years, and iodine-based tablets expire after six years. A few others have shorter or slightly longer shelf lives.
If you have tablets sitting in a kit somewhere, the trouble is remembering when you bought them and whether they still work.
There are other ways to clean water, like boiling it on the stove or running it through a LifeStraw, but tablets are usually faster and easier. Most use one of two chemicals, and each affects the water and your body a little differently. It is often fine to use tablets shortly after the date on the package. Below is how they work, how to keep them from expiring early, and when to throw them out.
How water purification tablets work
Water purification tablets kill the germs in untreated water that can make you sick. Using iodine, chlorine, or chlorine dioxide, they clean water from a mountain stream or water that got contaminated after an emergency. The chemicals deactivate the bacteria and viruses so the water is safe to drink.
Most tablets work by dropping them in the water and letting them dissolve. Many need to sit for thirty minutes or more. They get the job done, but a lot of them leave an off taste.
For iodine tablets, you can buy iodine taste neutralizer tablets (REI Products) that take the taste out, so the water feels normal again. For chlorine tablets, leave the container open and the chlorine evaporates, which brings the taste back to normal.
Tablets are a popular choice because they are light and need no special gear. That is why so many 72-hour emergency kits include them. Compared to boiling water or running it through a filter, tablets take up less space and work right away if you store them well.
How purification tablets stop working
Like most single-use products, tablets can stop working if you do not take care of them. A few things, including the weather, can make a tablet useless.
Natural expiration
When chemicals sit unused, the compounds slowly break down. Once they break down enough, they no longer deactivate the germs in the water. That is what expiration means. Most tablets have an expiration date a few years out from when they were made.
Exposure to the elements
The chemistry in a tablet is sensitive. A few things in the environment can make a tablet stop working before its printed date.
- Heat: extreme heat breaks down the chemicals faster than normal, so the tablets expire and quit working sooner than you expect.
- Moisture: if water touches a tablet before you use it, the chemicals break down faster and the tablet stops working.
- Sunlight: heat from the sun stirs up the chemicals and speeds up the breakdown.
- Air: air also makes tablets quit working sooner. That is why individually wrapped tablets tend to last longer than ones loose in a bottle. Air can also let outside contaminants get in, so do not open a tablet pouch until you plan to use it.
- Humidity: even if water never touches the tablets, warm air carrying a lot of moisture can make the chemicals unstable and leave you with a tablet that does not work.
Poor storage
Poor storage can be anything from a lid left loose to losing track of where the tablets have been. Stored badly, tablets can stop working and can even become a risk if you try to use them.
Container breakdown
Because tablets are so sensitive, the container has to stay in good shape. If the lid is not airtight or the container starts to rust, the tablets get contaminated and will not clean your water.
Are expired water purification tablets safe to use?
As noted above, most tablets use either chlorine or iodine, and both break down over time. Once the date on the package passes, you no longer know the chemical makeup of the tablets, so there is no way to say how well they will clean your water.
The chemicals themselves should not do your body serious harm, but the germs in the dirty water may still be there. That means you are not drinking clean water, which can make you sick.
Some people add more than the recommended number of tablets after the date passes, hoping the extra chemical will get the water clean. That is a bad idea. The chemicals may have broken down, but the larger dose going into your body can still hurt you. If your tablets are already expired, the safer move is to buy new ones.
Checking for expiration
What if you have a pile of tablets and cannot find the expiration date? If you really want to use them, there are a couple of quick tests to gauge how good they still are.
Squeeze test
Take one tablet between two fingers and squeeze. If it crumbles easily, the iodine or chlorine has broken down a lot, and the tablet is probably no good.
Discoloration
This one is for iodine tablets only. Iodine tablets are usually brown or gray. Yellow or greenish tablets have already broken down far and should be thrown out. It is a good habit to check the color before using one.
These tests help most with tablets in an open container. Once a container has been opened, the tablets expire much faster, usually within a year. The one tablet known to ignore these rules is Polar Pure (Amazon), which uses crystallized iodine and is less like a tablet.
Final thoughts
Most water purification tablets have an expiration date and stop working after it. They may be fine for a couple of months past that date, but tablets are cheap. The safest move is to buy fresh ones before your next hike. If you’d rather skip tablets altogether, purifying water with charcoal is another backup worth knowing.
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