Water purification tablets and drops: which type to choose (2026)
We compare water purification tablets and drops: chlorine dioxide, NaDCC (chlorine), chlorine with silver and iodine. Which germs they kill, how long to wait, how they taste, shelf life and who shouldn't use them.
In short
- For an emergency kit, chlorine dioxide tablets are the most complete choice: they kill bacteria, viruses and parasites, including Cryptosporidium, if you wait long enough.
- NaDCC (chlorine) tablets are cheap and fast but don't kill Cryptosporidium.
- Iodine tablets aren't suitable in pregnancy, for people with thyroid problems or for long-term use.
- No tablet removes cloudiness, heavy metals or chemicals. Clarify the water first and use a filter if needed.
Purification tablets are the smallest, lightest way to make water drinkable. A strip of 20 fits in a wallet and treats 20 quarts or more. They need no power, fire or maintenance. But they don’t all do the same thing.
The other methods (boiling, household bleach, filters) are in our water purification guide.
Tablet types compared
| Type | Bacteria | Viruses | Giardia | Cryptosporidium | Typical wait | Taste |
|---|---|---|---|---|---|---|
| Chlorine dioxide | Yes | Yes | Yes | Yes, with longer wait | 30 min – 4 hours | Mild |
| NaDCC (chlorine) | Yes | Yes | Partly | No | 30 min | Moderate chlorine |
| Chlorine + silver | Yes | Yes | Partly | No | 30 min – 2 hours | Chlorine |
| Iodine | Yes | Yes | Yes | No | 30 min | Strong, tinted water |
Actual times depend on the product, water temperature and cloudiness. Always follow the package instructions.
Which to choose
- For a go bag and emergency kit: chlorine dioxide. The most complete, with a mild taste.
- For large home volumes: NaDCC tablets, or plain unscented household bleach using the doses in our purification guide. Cheap.
- To keep already-treated water clean: silver-based tablets prevent recontamination for months, but aren’t fast disinfectants.
- Iodine: short term only; not for pregnant women, young children or people with thyroid conditions.
How to use them correctly
- Clarify cloudy water: let it settle and strain through a clean cloth or coffee filter.
- Use the right dose for the volume. More isn’t better.
- Shake and loosen the cap for a few seconds so treated water reaches the threads.
- Wait the stated time. In cold water (below 50 °F / 10 °C) or cloudy water, double it if the instructions allow.
- Store treated water in a clean, closed container.
What tablets don’t do
- They don’t remove chemicals, pesticides, fuel or heavy metals. Floodwater from industrial or farm areas isn’t made safe by tablets alone.
- They don’t clear cloudy water. Particles shield germs.
- They don’t replace stored water. They’re a backup for when your supply runs out.
How many to keep
Plan on 1 gallon (4 liters) per person per day. For a family of four for a week, that’s about 28 gallons (112 liters). Put a strip in each go bag and keep the rest with your stored water.
For filters, see our water filter guide.
Recommended equipment
What to look for when buying. Links go to partner shops; if you buy through them we may earn a small commission at no extra cost to you.Details.
Chlorine dioxide tablets
The most complete chemical protection: bacteria, viruses, Giardia and Cryptosporidium.
- Individually wrapped tablets
- Clear dose per liter/quart
- Shelf life of at least 3–5 years
NaDCC (chlorine) tablets
Cheap and fast, good against bacteria and viruses.
- Dose matched to your container size
- Sealed packaging
Two-part chlorine dioxide drops
For variable amounts of water; mixed just before use.
- Clear mixing instructions
- Leak-proof bottles
Frequently asked questions
How long do I wait after adding a tablet?
It depends on the type and the water. For chlorine dioxide, typically 30 minutes for bacteria and viruses and up to 4 hours for Cryptosporidium. For NaDCC, generally 30 minutes. Cold or cloudy water needs longer. Follow the package instructions exactly.
How long do tablets last?
Usually 3–5 years in the original packaging, kept dry and away from heat. The expiry date is on the pack. Once the foil is opened, tablets degrade faster, so choose individually wrapped tablets.
Tablets or a filter?
Ideally both. Filters remove particles, bacteria and parasites, but many don't stop viruses. Tablets kill viruses but don't clear cloudy water. Used together, filter first, then tablet, they cover almost any situation. See our water filter guide.
Sources and further reading
Preper is for general education and does not replace instructions from your local authorities or advice from a doctor. In an emergency, call your local emergency number.