Water purification tablets: the right dose, then wait
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Quick answer
Water purification tablets release a disinfectant, usually chlorine, chlorine dioxide or iodine, that kills most germs in clear water after a waiting time. EPA says tablet strengths differ, so follow the label. Aquatabs, for example, uses one 49 mg tablet per half-gallon and a 30-minute wait. Filter cloudy water first. Tablets do not remove chemicals: EPA says disinfection will not destroy heavy metals, salts and most other chemicals.
Chlorine, chlorine dioxide or iodine
| Type | What sources say | Watch for |
|---|---|---|
| Chlorine (NaDCC, as in Aquatabs) | Aquatabs reports 99.9999% bacteria, 99.99% virus and 99.9% Giardia cyst reductions in clear water within 30 minutes, using the US EPA purifier challenge protocol | CDC says chemical disinfectants may not kill all parasites |
| Chlorine dioxide | CDC says it can kill Giardia and is somewhat effective on Cryptosporidium | Still safest to filter first, CDC says |
| Iodine | EPA lists iodine among tablet options | CDC says people who are pregnant, have thyroid problems or are iodine-sensitive should avoid it, and no one should use it for more than a few weeks at a time |
EPA's emergency page lists tablets containing chlorine, iodine, chlorine dioxide or other disinfecting agents and says each product may have a different strength.
How to use tablets, step by step
- Check the water: Aquatabs says to use its tablets in water above 40°F.
- Pre-filter cloudy water: EPA says to let cloudy water settle and filter it through a clean cloth, paper towel or coffee filter.
- Dose by volume: follow your tablet's label; Aquatabs lists 49 mg for a half-gallon and 397 mg for up to 4 gallons.
- Dissolve and cover: stir or shake until dissolved, then cover the container.
- Wait: Aquatabs says 30 minutes before drinking; other products set their own times.
- Do not add to boiling water: Aquatabs says lukewarm water is fine but boiling is not recommended.
Aquatabs says that in a closed container its tablets keep protecting for at least 24 hours by releasing more chlorine as needed.
How many tablets you need
Using Aquatabs' doses as an example:
- 1 gallon: two 49 mg tablets.
- 4 gallons: one 397 mg tablet, or eight 49 mg tablets.
- A 100-count pack of 49 mg tablets: treats 50 gallons.
Small tablets suit bottles and bags on the move; large tablets suit a bucket or jug at home. Count against your water plan; see our emergency water storage guide for how much to store.
Do water purification tablets expire?
- Yes: Aquatabs lists up to 5 years from manufacture for strip-packed 49 mg tablets and up to 3 years for tub-packed 397 mg tablets.
- Where to look: the expiry date is on the back of every strip and on the side of tubs, Aquatabs says.
- Storage: protect tablets from temperature extremes and high humidity.
- Check it worked: Aquatabs says chlorine test strips show the ppm level of treated water.
Tablets, filters or boiling
- Boiling: EPA says a rolling boil for at least one minute, or three minutes above 5,000 feet, kills pathogenic bacteria, viruses and protozoa.
- Bleach: EPA's table lists 8 drops of 6% unscented bleach per gallon, with a 30-minute wait.
- Filters: CDC advises filtering first, then disinfecting, because chemical disinfectants may not kill every parasite; see our portable water filter and Sawyer Squeeze guides.
- Chemicals: none of these removes heavy metals, salts or most chemicals, per EPA. If you suspect fuel or chemical contamination, use stored or bottled water.
A filter plus tablets covers the widest range of germs for stream or flood-area water.
What to look for when you buy
Bottle-sized doses: Aquatabs 49 mg tablets
Best for: Go-bags, car kits and treating a water bottle or half-gallon at a time
Aquatabs lists one tablet per half-gallon, a 30-minute wait, NaDCC chlorine with no iodine, strip packs good for up to 5 years from manufacture and expiry dates printed on each strip.
Watch out: Filter cloudy water first; chlorine alone may not handle every parasite.
See options on Amazon (opens Amazon in a new tab)Bucket-sized doses: Aquatabs 397 mg tablets
Best for: Treating stored water in 4-gallon batches at home
Aquatabs lists one tablet for up to 4 gallons with the same 30-minute wait, in tubs good for up to 3 years from manufacture.
Watch out: Too strong for a single bottle; keep the 49 mg size for small containers.
See options on Amazon (opens Amazon in a new tab)Confirm the dose: free chlorine test strips
Best for: Checking that treated water carries chlorine before drinking
Aquatabs says chlorine test strips show the ppm level of water it has disinfected, a quick check when you are unsure of a dose.
Watch out: Match the strip's range to drinking water levels; strips also expire.
See options on Amazon (opens Amazon in a new tab)Questions people ask
- How do water purification tablets work?
- They release a disinfectant such as chlorine; Aquatabs says its NaDCC tablets disinfect clear water within 30 minutes.
- Do water purification tablets expire?
- Yes; Aquatabs lists up to 5 years for strips and up to 3 years for tubs, with the date printed on the pack.
- How do you use water purification tablets?
- Pre-filter cloudy water, add the labeled dose for the volume, stir, cover and wait the stated time.
- Do tablets make any water safe?
- No; EPA says disinfection will not remove heavy metals, salts and most other chemicals.
Sources
- Emergency Disinfection of Drinking Water, U.S. Environmental Protection Agency
- Water Treatment Options When Hiking, Camping or Traveling, Centers for Disease Control and Prevention
- Aquatabs Tablets, Aquatabs
- Frequently Asked Questions, Aquatabs
- Aquatabs 49mg Tablets, Aquatabs US
- How to Use Aquatabs, Aquatabs US