These do what they're supposed to do. Before I give a review, I'll quote the box on a few points.1. For use only when drinking water is suspected or known to be bacteriologically substandard. Not to be used on a continuous basis. (Their website suggests a six-week limit.)2. Unopened bottles should remain effective for four years. (Look at the bottom of this review for how to date your tablets.)3. We recommend that you do not keep an opened bottle for more than one year.4. 2 tablets make one quart of bacteriologically water suitable to drink.5. Proven effective against Giarda Lamblia when used as directed.6. Has not been shown to inactivate Cryptosporidium cysts.In a nutshell, use according to the directions and you'll be just fine. The bottle contains 50 tablets; you use two per quart of water. In really murky water, I use three. The active ingredient is Tetraglycine Hydroperiodide 16.7% and each tablet contains 6.68% of Titratable Iodine. This is the same stuff that I used in the military, but just to be sure, I opened a bottle and got three quarts of water from the Ohio River. Murky stuff. The first quart was treated with just the Potable Aqua (2-1/2 tablets). The second quart was boiled for ten minutes. The third quart was boiled for ten minutes, then given two tablets of Potable Aqua. All water was filtered through an untreated handkerchief first to remove debris and sediment. I'll note that my measurements were three quarts before boiling, so I'm sure some of the water was lost in the last two quarts due to the boiling process. The results?While none of the water was as good as tap water, I'm still alive. The first batch (just Potable Aqua) was okay. I remember Potable Aqua having a bad taste; so bad that they included a separate bottle of pills to add that made the taste more bearable. That other bottle is unnecessary here. The water definitely had a chemical taste, but I could drink the minimum of a gallon a day if I needed to.The second batch (just boiling, no pills) tasted better, but smelled bad. I would be hesitant to drink any more than necessary.The third batch (boiled, then treated with Potable Aqua) was obviously the best. Considering that boiling only took ten minutes and a metal water bottle, this is the best option. Remember that all of the water was filtered through a handkerchief first to get rid of any sediment, debris, bugs, etc.I'll guess that if you filter the water, then boil, then use the tablets, you can use only one tablet. I'm not a doctor, dietician, or representative of the company, but I do have extensive training in SERE operations and I've been using these tablets for over fifteen years.How can you find out when your pills were made? Each bottle has a series of numbers imprinted. For example: 403127. The first number is the month; in this case, the fourth month is April. The second and third numbers are the last two of the year; in this case, 2003. These pills were made in April of 2003. The last three numbers (127) indicate that this was the 127th batch made in that time frame. The code can be five or six numbers long; the first three numbers always denote the month and year; the last two or three always denote the batch number.I contacted the company. Made 11/2021. Company says no expiration date - grayish brown is good, yellowish/green should be replaced. Another source says 4 - 5 years.There are two major approaches to purifying contaminated water: you can try to trap sediment and microorganisms via a filter, or you can use various methods to sterilize the water by killing anything living in it.For absolute safety, some recommend doing both, so I'm not going to sit and compare tablets to a pump filter, as they are different mechanisms of purification that aren't necessarily competitors. In fact, regardless of how you kill the bugs in your water, I recommend at the very least running the water through a cloth/bandana first as a first step in removing dirt and larger microorganisms.That gives these tablets three major competitors...The first, and cheapest, competitor is good old-fashioned boiling of water. In fact, boiling kills most things that some chemicals might not even get to. The downside, of course, is the need to start a fire, wait, and boil water. Good if you're camping overnight and prepping for the next day, but not so great if you need to fill up in the middle of a several-hour trek. If you're the kind of person who carries a mini-burner and a stove-top anyway, you probably don't need these tablets.The second, and most expensive, competitors are the UV light devices that sterilize using light. It sounds like nonsense, but it does in fact work. The problem is the cost and reliability. Sure, it can be argued that if you break down the cost per liter of water of a sterilizing pen is actually lower than using tablets, but that's only assuming that you actually get the maximum number of cycles that the manufacturer claims it is good for, and it ignores the cost of the batteries and the reliability of the products. From my experience (luckily, not with gear that I had to pay for), the SteriPEN is finicky from time to time. Unless you're doing light day-hikes, I wouldn't rely on batteries and electronics to hold up. Especially over years of hard use and being banged around in a backpack. It's nice having neat technology to show off, but nobody will be impressed when your magic light is broken and you're crapping your pants (literally).The third source of competition is other tablets/drops. There are several types, and while some tout better flavor, more effectiveness, etc, it really comes down to whether it'll kill the bugs in whatever area you're hiking. In other words: most of them are the same unless you're headed to an area with a very specific rare microorganism that certain tablets won't kill. These have held up for me through years of trekking on four different continents. That's quite good enough for me. The taste, sure, is a bit off, but it's nothing unbearable. Between tablets, I don't have much of a preference, but I do prefer tablets over liquid drops, as they're easier to carry and use.Small, light, and easy to carry, this product a must have even if you use a water filter. I look at this product as an extra layer of protection. Often many forget to use filtered drinking water to clean dishes or for personal hygiene. This product ensures any water you use is most assuredly safe, not just your filtered drinking water.If need tablets to purify water and do not care about taste this is the product that works. Used on India trip where there was no bottled water for days. Fit inside my backpack. Could see impurities taken out of water. Did not get sick. Recommend with other tablets to neutralize iodine taste.Small easy to carry bottle that assures germ free water when there is no bottled water available. I must for wilderness or bug out time. Avoids terrible illnesses.Great product and qualityi sure hope i never need this- but very glad i have several of them in case of an emergency-Very fast shipping and packaging is just like the picture but haven't opened or tried them yet so will have to wait and see. I did read adding vitamin c in the water can help neutralize the iodine taste but only after 34 minutes when the iodine is finished working/purifying.********************************************************************Some other comments about it on the internet....The chemical name for vitamin C is ascorbic acid. When Iodine and ascorbic acid are combined in solution, a chemical reaction takes place. In this chemical reaction, the ascorbic acid molecule loses electrons, which are transferred to the iodine molecule. Chemists call this type of reaction an oxidation/reduction reaction (or redox reaction for short). The ascorbic acid is oxidized to dehydroascorbic acid, and the iodine is reduced to Iodide ions. Oxidation-reduction reactions always occur in pairs like this. The molecule that loses electrons is oxidized, and the molecule that accepts the electrons is reduced.************************************************************************Guess what else - it is an instantaneous chemical reaction. The ascorbic acid complexes the iodine on contact, removing both taste and color. Try it in a clear container. Watch the color disappear entirely before your eyes in a heartbeat when you invert the container to mix it. That color change tells you it's done.There is an important caveat: it only takes a VERY tiny amount (fits easily on the tip of a knife blade) of ground-up vitamin C tablet to do this in an entire gallon of water. Be advised that you will always add more than you really needed. No big deal UNLESS you forget to thoroughly rinse the water container before you add iodine the next time.I love the fact that this purifier is in such a small container that you can carry it wherever you go. brilliantHope I never need themJust in caseAs described ??