Water · Water Treatment
Chemical backup when your filter breaks, your power is out, or your stored water runs low. Three chemistries, different strengths, one job.
The basics
Water purification tablets are small, lightweight chemical disinfectants that make questionable water safer to drink. You drop a tablet into a container of water, wait for the specified contact time, and the active ingredient kills bacteria, viruses, and (depending on the chemistry) parasites like Giardia and Cryptosporidium.
Most households that take water preparedness seriously will use a gravity filter or stored water as their primary system. Tablets serve a different role: they are the backup. They weigh almost nothing, fit in a drawer or a ready bag, cost less than a dinner out, and work when nothing else does. If your filter breaks, if you need to treat water from an unfamiliar source during an evacuation, or if a boil-water advisory hits and you have no way to boil, tablets are the fallback that fits in your pocket.
The catch is that not all tablets are the same. Three different chemistries are sold as "water purification tablets," and they vary in what they kill, how long they take, and who should avoid them. Choosing the wrong one leaves gaps. This page walks through all three, so you can stock the right chemistry for your situation.
Quantity guidance
Plan on roughly 3 liters of drinking water per person per day. Most tablets treat 1 liter each. From there, the math scales by household size and the duration you are preparing for.
| Scenario | Per person | Family of 4 |
|---|---|---|
| 72-hour supply | 9 tablets | 36 tablets |
| 2-week supply | 42 tablets | 168 tablets |
| Recommended baseline | 50–100 tablets | 200–400 tablets |
A note on role: Tablets are a backup to mechanical filtration and stored water, not a standalone primary treatment for most households. If you already have a gravity filter and stored water, a pack of 30 to 50 chlorine dioxide tablets per person covers the gap. If tablets are your only treatment method, stock more generously.
Storage
Store tablets in their original sealed packaging in a cool, dry location away from direct sunlight. A kitchen drawer, closet shelf, or the same bin as your water storage supplies works well. Avoid garages or sheds where temperature swings are extreme.
Most unopened tablets last 4 to 5 years. Individually foil-wrapped tablets (like Katadyn Micropur MP1) tend to hold potency longer than tablets packed loose in a bottle, because each tablet stays sealed until you use it. Once a bottle is opened, moisture exposure begins to degrade the remaining tablets.
Write the purchase date on the packaging with a permanent marker. Check your supply every 12 months when you rotate other consumables. Replace any pack that has passed its printed expiration date.
Expired tablets lose potency gradually. They do not become toxic, but the active ingredient degrades, meaning the tablet may no longer produce enough disinfectant to fully treat the water. In an emergency, an expired tablet is better than untreated water, but for planned preparedness, there is no reason to keep expired stock. Replace and rotate on schedule.
Chemistry comparison
The label "water purification tablet" covers three distinct active ingredients. Each has different coverage, wait times, and restrictions. Brand matters here because the chemistry determines what the tablet can and cannot do.
The broadest-spectrum tablet chemistry. The only tablet type that kills Cryptosporidium.
NWS top pick chemistry
Fast-acting chlorine-based chemistry. Used by relief organizations worldwide. Does not cover Crypto.
NWS budget pick chemistry
Older chemistry. Effective against bacteria and viruses but carries medical restrictions and a strong taste.
Use only if others unavailable
NWS recommendation: Stock chlorine dioxide tablets as your primary. They cost a few dollars more per pack but cover every pathogen, including Cryptosporidium. If you want a cheaper backup to pair with a mechanical filter that already removes parasites, NaDCC tablets (Aquatabs) are a solid second option at roughly half the price.
Safety
Every tablet type has specific dosing and contact time requirements printed on the package. Follow them exactly. Overdosing does not make water safer, and underdosing leaves pathogens alive. The table below summarizes the key numbers across all three chemistries.
| Product | Chemistry | Dose | Wait (bacteria) | Wait (Crypto) |
|---|---|---|---|---|
| Katadyn Micropur MP1 | Chlorine dioxide | 1 tablet / 1 L | 30 min | 4 hours |
| Aquatabs (49 mg) | NaDCC | 1 tablet / 1 L | 30 min | Not effective |
| Potable Aqua (iodine) | Iodine | 2 tablets / 1 L | 30 min | Not effective |
Dosing data per manufacturer instructions. Wait times for Cryptosporidium per CDC guidance (CDC: How to Make Water Safe in an Emergency). Last verified June 2026.
Chlorine dioxide and NaDCC tablets have no known medical restrictions for the general population. Iodine is different. Per the CDC, avoid drinking water disinfected with iodine if you are pregnant, have thyroid problems, or have a hypersensitivity to iodine. Nobody should drink iodine-treated water for more than a few weeks at a time.
Chemical disinfectants work best in clear water. If the water source is cloudy, filter it first through a clean cloth, bandanna, or coffee filter, then treat with tablets. Particles in the water can shield pathogens from the chemical, reducing effectiveness. If you cannot filter first, let the water sit until sediment settles, pour off the clear water, and then add the tablet.
Where to buy
Top pick
Chlorine dioxide tablets
Individually foil-wrapped. Kills bacteria, viruses, Giardia, and Cryptosporidium. EPA-registered. 4-hour wait for full Crypto coverage, 30 minutes for everything else. 5-year shelf life unopened. The most complete tablet on the market.
$12 – $18 per 30-count pack
Budget pick
NaDCC tablets
NSF/ANSI 60 certified. Used by humanitarian organizations worldwide. Kills bacteria, viruses, and Giardia in 30 minutes with virtually no taste. Does not kill Cryptosporidium. Best paired with a mechanical filter that handles parasites.
$8 – $12 per 50-count pack
Affiliate disclosure: New World Survival earns a small commission on purchases made through links on this page, at no cost to you. We only recommend products we would stock in our own kit.
Related
Purification tablets are one layer in a broader water preparedness system. Most households benefit from combining stored water, a gravity or portable filter, and chemical backup tablets. Each covers a different failure mode. The pages below connect to the rest of the system.