Water purification tablets vs filters: which should you keep?
For a home emergency kit, keep stored water first, a pack of purification tablets second, and a filter if you want a reusable backup. Boiling is the most reliable way to kill germs when you have heat. Tablets kill bacteria and viruses but act slowly on some parasites; filters remove bacteria and parasites but most do not stop viruses. None of them removes chemical pollution.
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The comparison at a glance
| Method | Bacteria | Viruses | Protozoa (Giardia, Crypto) | Chemicals | Time | Needs |
|---|---|---|---|---|---|---|
| Boiling | Yes | Yes | Yes | No | 1 min rolling boil + cooling | Fuel and a pot |
| Chlorine tablets (NaDCC) | Yes | Yes | Giardia yes; Crypto poorly | No | ≈ 30 min | Clear water |
| Chlorine dioxide tablets | Yes | Yes | Yes, given enough time | No | 30 min to several hours | Clear water, patience |
| Hollow-fibre filter (0.1 µm) | Yes | Mostly no | Yes | No (unless carbon stage) | Immediate | Squeezing or gravity |
| Household bleach | Yes | Yes | Giardia yes; Crypto poorly | No | 30 min | Unscented bleach, dropper |
| Activated carbon | No | No | No | Some, plus taste | Immediate | Combine with another method |
Times are typical; always follow the instructions on the product you use. Sources: US EPA, WHO emergency guidance and manufacturer instructions.
Boiling: the gold standard
The US Environmental Protection Agency says boiling is sufficient to kill pathogenic bacteria, viruses and protozoa. Bring water to a rolling boil for at least one minute (three minutes at high altitude), let it cool, and store it covered. Dutch water companies ask people to boil emergency water for three minutes; if you get an official boil-water notice, follow it. The drawback is fuel: boiling a family’s drinking water takes a lot of gas, and stoves must be used outdoors.
Purification tablets
Tablets are the lightest and cheapest backup. There are two main types:
- Chlorine-based (NaDCC) tablets kill bacteria and viruses in about 30 minutes, but are weak against Cryptosporidium, a parasite with a tough shell.
- Chlorine dioxide tablets also deal with Cryptosporidium, but need longer contact time; manufacturers commonly specify up to four hours for full protection.
Both work best on clear water. If water is cloudy, let it settle and pour it through a clean cloth or coffee filter first. Tablets leave a slight taste, which you can reduce by pouring water between two clean containers.
Portable filters
Hollow-fibre filters with 0.1-micron pores, such as the Sawyer Squeeze and LifeStraw, remove bacteria and protozoa instantly and can filter hundreds or thousands of litres before they wear out. Most do not remove viruses, which are far smaller. In Europe, North America and other places where water is usually safe and viruses in fresh water are less common, a filter is a sensible backup; where viral contamination is a concern, combine a filter with tablets or boiling.
- Straw filters: drink directly from the source. Simple, but you can’t fill a pot.
- Squeeze filters: fill a pouch and squeeze into a bottle or pan. The most versatile.
- Gravity filters: hang a bag and let it drip. Best for a family.
Don’t let hollow-fibre filters freeze once they have been used: ice can damage the fibres without any visible sign. Keep used filters indoors in winter.
What none of them fix
No tablet, filter or boiling removes fuel, pesticides, heavy metals or industrial chemicals. After floods or chemical incidents, follow official advice and drink only stored or supplied water. If authorities tell you not to use tap water at all, boiling won’t help.
Our picks
| Product | Best for | Key spec | Buy |
|---|---|---|---|
| Water purification tablets | Every kit, cheapest backup | Light, long shelf life | Check price on Amazon |
| Chlorine dioxide tablets (Micropur MP1) | Broader protection | Works on Cryptosporidium with time | Check price on Amazon |
| Sawyer Squeeze | Reusable all-round filter | 0.1 µm hollow fibre | Check price on Amazon |
| LifeStraw personal filter | Grab bag, simplest option | Drink directly through it | Check price on Amazon |
| Gravity water filter | Families, larger volumes | Hangs and drips, hands-free | Check price on Amazon |
| Camping stove | Boiling water outdoors | Gas cartridge | Check price on Amazon |
We don’t list prices because they change often. Use the button to see the current price on Amazon.
What we recommend
- Store water first: at least 9 litres (2.4 US gal) per person. Treatment is the backup, not the plan.
- Add a pack of tablets to the 72-hour kit. They are inexpensive and last years.
- Add a squeeze filter if you hike or camp, or want a reusable option for a longer emergency.
- Keep a stove and gas for boiling, used outdoors only.
Tablets and a filter are also on our flood kit and grab-and-go bag lists.
Questions people ask
Are water purification tablets safe?
Yes, when used as directed. Follow the dose and contact time on the pack, and use them only on clear water: filter or settle cloudy water first.
Do water filters remove viruses?
Most portable filters with 0.1–0.2 micron pores remove bacteria and protozoa but not viruses, which are much smaller. Purifiers that use very fine membranes or combine a filter with chemical treatment do. Check the product’s claims.
How long should I boil water to make it safe?
Bring it to a rolling boil for at least one minute; three minutes at high altitude. Follow any official boil-water notice, which may specify longer.
Can I drink flood water if I filter or boil it?
No. Flood water can contain fuel, chemicals and sewage. Boiling and filtering don’t remove chemicals. Use stored water or emergency supplies from the authorities.
Which is best for a 72-hour kit?
Stored water first. Then a pack of tablets as a cheap, light backup. Add a filter if you want a reusable option or also go hiking and camping.
Keep reading
- How much water to store for 72 hours
- /kits/flood/
- /kits/evacuation-bag/
- 72-hour emergency food list (no cooking)