Best gravity water filters for emergencies
The CDC says a filter needs an absolute pore size of 0.3 micron or smaller to remove bacteria and 1 micron or smaller to remove parasites, and that portable filters will not remove viruses, so add a chemical disinfectant after filtering. For a home emergency, choose a gravity filter that states an absolute pore size of 0.2 micron or smaller, or a purifier that claims the NSF P231 standard for viruses, and check any certification in NSF's own listings.
The CDC estimates that germs spread through water caused 7.15 million illnesses, 118,000 hospital stays and 6,630 deaths in the US in a single year (2014).
Our picks at a glance
| Product | Best for | Key specs | |
|---|---|---|---|
| LifeStraw Peak Series Gravity Purifier (8L) | Best overall | 8 L (2.1 gal) bag, up to 30 L per hour, 0.02 micron, filter life up to 18,000 L, no power needed | Check price |
| LifeStraw Mission (12L) | Biggest bag | 12 L bag, up to 12 L (3.1 gal) per hour, 0.02 micron, filter life up to 18,000 L (4,755 gal) | Check price |
| LifeStraw Community | Large households, groups | 50 L tank, 0.02 micron, filter life up to 100,000 L (26,000 gal) | Check price |
| British Berkefeld Gravity System with Ultra Sterasyl filters | Countertop, NSF certified | 6 L, 8.5 L or 12 L stainless tank, 2 ceramic candles, candles last up to 6 months (Doulton) | Check price |
| Katadyn BeFree Gravity 6L | Light and fast | 6 L bag, 0.1 micron, up to 2 L per minute, filter capacity up to 1,000 L, about 263 g | Check price |
LifeStraw Peak Series Gravity Purifier (8L)
A fast gravity bag with a 0.02 micron filter that LifeStraw says removes viruses as well as bacteria and parasites, and meets US EPA and NSF P231 standards. It is the quickest of the virus-rated bags we looked at.
Key specs: 8 L (2.1 gal) bag, up to 30 L per hour, 0.02 micron, filter life up to 18,000 L, no power needed
Watch out for: No carbon stage for taste or chemicals, and the replacement filter was listed as sold out on LifeStraw's site when we checked.
Check price on AmazonLifeStraw Mission (12L)
The 12 liter bag holds more dirty water per fill, and LifeStraw says it removes 99.999% of viruses and meets NSF P231 for viruses, bacteria and parasites.
Key specs: 12 L bag, up to 12 L (3.1 gal) per hour, 0.02 micron, filter life up to 18,000 L (4,755 gal)
Watch out for: Less than half the flow rate of the Peak Series, so filtering a day's water for a family takes longer.
Check price on AmazonLifeStraw Community
A 50 liter tank built for groups. LifeStraw says the filter lasts up to 100,000 liters and meets NSF P231 for viruses, bacteria and parasites.
Key specs: 50 L tank, 0.02 micron, filter life up to 100,000 L (26,000 gal)
Watch out for: Large, heavy and costs several times more than a bag purifier. The replacement cartridge was listed as sold out when we checked.
Check price on AmazonBritish Berkefeld Gravity System with Ultra Sterasyl filters
A stainless steel countertop filter that is independently certified: NSF lists the British Berkefeld Ultra Sterasyl under NSF/ANSI 53 for cyst and turbidity reduction. That is the standard the CDC points to for removing parasites.
Key specs: 6 L, 8.5 L or 12 L stainless tank, 2 ceramic candles, candles last up to 6 months (Doulton)
Watch out for: The NSF listing covers cysts (parasites), not bacteria or viruses, so disinfect the water after filtering as the CDC advises.
Check price on AmazonKatadyn BeFree Gravity 6L
Light enough for a go-bag and fast. Katadyn says its 0.1 micron filter removes bacteria, cysts and sediment, which meets the CDC's pore-size rule for both bacteria and parasites.
Key specs: 6 L bag, 0.1 micron, up to 2 L per minute, filter capacity up to 1,000 L, about 263 g
Watch out for: Does not remove viruses, and the filter's 1,000 liter life is short next to the purifiers above.
Check price on Amazon- What to look for
- Certified versus claimed: what we found
- How much water your filter needs to handle
- How to use it safely
- Why Berkey is not on this list
- Gear
What to look for
Most of what decides whether a filter makes water safe is printed on the box, if you know what to read. This table is built on the CDC's emergency water guidance, the CDC's guide to choosing home filters and NSF's list of water treatment standards.
| Check | What you want | Why |
|---|---|---|
| Pore size | 0.3 micron absolute or smaller | The CDC says 0.3 micron absolute removes bacteria and 1 micron absolute removes parasites such as Giardia and Cryptosporidium. "Nominal" or "mean" sizes let bigger things through some holes. |
| Viruses | A purifier claim to NSF P231, or disinfect after | The CDC says portable filters will not remove viruses, so add iodine, chlorine or chlorine dioxide afterwards. NSF P231 covers microbiological purifiers, based on the EPA's guide standard. |
| Parasites | NSF/ANSI 53 (or 58) for cyst reduction | The CDC names these two standards for filters that remove parasites. |
| Taste only | Do not rely on NSF/ANSI 42 alone | NSF says 42 covers taste, odor and chlorine, not germs. NSF/ANSI 401 covers some emerging chemicals, also not germs. |
| Certified or "tested to" | A listing in NSF's own database | The CDC says look for the NSF mark on the label and check the listing. A maker saying it "meets" a standard is not the same as a certification. |
| Chemicals | Another water source | The CDC says boiling and bleach cannot fix water with fuel or toxic chemicals in it, and germ filters are not built for it either. Platypus, for example, says its gravity filter does not remove chemicals. |
| Upkeep | Spare filters on the shelf | The CDC says change filters when the maker says, or germs can grow in them. |
Certified versus claimed: what we found
We searched NSF's public listings for every brand on this page in November 2026.
- British Berkefeld (Doulton): NSF lists the Ultra Sterasyl gravity system under NSF/ANSI 53 for cyst and turbidity reduction.
- LifeStraw: LifeStraw says its purifiers meet NSF P231. A search of NSF's listings under the LifeStraw name returned no matching products, so treat that as the maker's own claim.
- Katadyn: Katadyn's factsheet gives the pore size but names no NSF standard.
If you are unsure what your filter removes, do what the CDC says and add a disinfectant after filtering.
How much water your filter needs to handle
The CDC says plan on at least 1 gallon per person per day. For a family of 4 over 2 weeks, that is 56 gallons, or about 212 liters (our math). Every filter here with a liter rating is rated above that, but bag filters only hold 6 to 12 liters at a time, so you will be refilling them several times a day. See how much water to store.
How to use it safely
- Start with the clearest water you can get. Let cloudy water settle, or pour it through a clean cloth or coffee filter first (CDC).
- Skip water that smells of fuel or chemicals. The CDC says boiling and bleach will not make it safe. Find another source.
- Filter, then disinfect. Unless your purifier is rated for viruses, add a chemical disinfectant after filtering (CDC). See how to make water safe to drink for bleach amounts.
- Keep dirty and clean sides apart. Use separate containers for dirty and filtered water, and follow the maker's instructions for cleaning or backflushing.
- Change filters on time, with gloves. The CDC says wear gloves and wash your hands after, and people with weak immune systems should get someone else to do it.
Why Berkey is not on this list
Many people ask about Berkey, so here are the facts we found. The EPA issued orders telling sellers to stop selling Black Berkey filter products, including the Big, Royal, Imperial and Crown systems. The EPA's orders say the products are unregistered and misbranded pesticides under federal law, because of their silver and germ-killing claims (EPA order to Berkey Filters, EPA order to Berkey International).
A search of NSF's certified listings for "Berkey" returned no matching products when we checked in November 2026. With other filters available that state their pore size clearly or hold an NSF listing, we left Berkey out.
Common mistakes
- Buying a filter that gives a nominal pore size instead of an absolute one.
- Assuming a filter removes viruses. The CDC says portable filters do not, so disinfect after filtering.
- Trusting an NSF/ANSI 42 mark for safety. It covers taste and odor, not germs.
- Taking a maker's 'meets NSF standards' line as a certification without checking NSF's listings.
- Filtering water that smells of fuel or chemicals. Germ filters and boiling will not fix it.
- Running muddy water straight through. Let it settle or pre-filter it first.
- Having no spare filter. Replacement filters for several picks were sold out when we checked.
Gear for this
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Unscented bleach and a glass eye dropper
For disinfecting after filtering, which the CDC says to do with portable filters.
Chlorine dioxide tablets
A lighter disinfectant option for after filtering. The CDC lists chlorine dioxide as one to use.
Food-grade water containers with lids
So filtered water never goes back into a dirty bucket.
Coffee filters
For pre-filtering cloudy water, as the CDC suggests, so your filter does not clog.
Disposable gloves
The CDC says wear gloves when you change filters.
Questions people ask
Do gravity water filters remove viruses?
Most do not. The CDC says portable filters will not remove viruses, so add a chemical disinfectant after filtering. Some purifiers, such as LifeStraw's, claim to meet NSF P231 for viruses.
What micron water filter do I need for emergencies?
The CDC says an absolute pore size of 0.3 micron or smaller to remove bacteria and 1 micron or smaller to remove parasites. Look for the word absolute, not nominal.
Is Berkey NSF certified?
A search of NSF's certified listings for Berkey returned no matching products in November 2026. The EPA has also issued stop-sale orders on Black Berkey filter products, calling them unregistered pesticides.
Sources
- CDC: How to Make Water Safe in an Emergency
- CDC: About Choosing Home Water Filters
- CDC: Waterborne Disease in the US, results
- NSF: Standards for Water Treatment Systems
- NSF listings: Doulton
- NSF listings: Berkey
- NSF listings: LifeStraw
- EPA: Stop sale order, Berkey Filters
- EPA: Stop sale order, Berkey International
- LifeStraw: Peak Series Gravity Purifier
- LifeStraw: Mission
- LifeStraw: Community
- Doulton: British Berkefeld Gravity System, Ultra Sterasyl
- Katadyn: BeFree Gravity 6.0L factsheet
- Platypus: GravityWorks Water Filter System
- CDC: How to Create and Store an Emergency Water Supply
Related entries
- W-01How to make water safe to drink in an emergencyBoil it, bleach it, or filter and treat it. Exact amounts from the CDC.
- W-02How much water to store for an emergency1 gallon per person per day. Work out your household total in 10 seconds.
- W-03Emergency water sources in your homeYour water heater, pipes, ice and toilet tank hold water you can use. What to avoid.
- G-04Best freeze-dried emergency foodCount calories, not servings. Kits compared on calories, shelf life, water to cook and storage.
General safety information only, not medical or professional advice. Rules can change, so check the linked sources and follow your local officials. As an Amazon Associate I earn from qualifying purchases.