Best gravity water filters

Four gravity filters, compared on what their makers publish. We have not tested them. A gravity filter suits a household or a group: you fill a bag, hang it up, and water runs through the filter on its own.

Specifications last checked November 9, 2026. How we evaluate · Corrections and updates · Portable filters guide

How a gravity filter works, and its limits

You fill an upper bag with untreated water and hang it above the filter. Gravity pushes the water through a hollow-fiber membrane into a clean bag or container below. There is nothing to pump.

The CDC's guidance on making water safe in an emergency sets the limits, and they apply here as they do to any portable filter:

• Viruses. Portable filters will not remove viruses. The CDC says to add a disinfectant such as chlorine, iodine or chlorine dioxide after filtering.
• Pore size. An absolute pore size of 0.3 micron or smaller removes bacteria, and 1 micron or smaller removes parasites such as Giardia or Cryptosporidium. All four filters below list 0.1 or 0.2 micron.
• Chemicals. Water with fuel or toxic chemicals cannot be made safe by boiling or disinfecting. Use bottled water or another source.

Boiling is still the CDC's best method. Ready.gov says to store at least one gallon of water per person per day. A gravity filter is for when that stored water is gone.

Quick answer

These are comparisons of published figures. Which one fits depends on how many people you need to supply and how far you will carry it.

The four models, one by one

Platypus GravityWorks

The 4.0 L version weighs 11.5 oz (326 g) and has a 0.2 micron hollow-fiber filter rated for 1,500 L at up to 1.75 L a minute. The total capacity is 8 L, split between a 4 L dirty bag and a 4 L clean bag. A 6.0 L version holds 12 L and weighs 12.3 oz (349 g), with the same filter specifications. Cascade Designs says each microfilter is individually tested to meet EPA and NSF guidelines for removing 99.9999% of bacteria and 99.9% of protozoa, and that you can backflush it in about 4 seconds. We did not read its warranty terms.

Platypus QuickDraw 3L Gravity

It is a 3 L system that weighs 8.2 oz (233 g) in total, and its spec table lists a minimum weight of 4.8 oz (136 g). The 0.2 micron filter is rated for 1,000 L, the shortest life of the four by rating. Flow is 1.75 L a minute by gravity and 3 L a minute with squeeze pressure. Cascade Designs makes the same EPA and NSF testing claim as for the GravityWorks. We did not read its warranty terms.

Sawyer One Gallon Gravity

The kit has a 1-gallon bladder, the MINI filter (about 2 oz on its own), a cleaning plunger and a hose, and weighs 11.8 oz. The membrane is 0.1 micron absolute, and Sawyer rates the filter for up to 100,000 gallons. It lists 99.99999% bacteria and 99.9999% protozoa removal. Sawyer says it can filter water for a group in as little as 7 minutes, and gives no flow rate in liters. Its backwashing advice depends on the water: about every 1,000 gallons for clear water, every 10 gallons for very muddy water. We did not read its warranty terms.

LifeStraw Peak Series Gravity 3L

It weighs 8.1 oz (228 g), flows at 1.7 L a minute and has a 0.2 micron membrane rated for 2,000 L (500 gallons). LifeStraw lists 99.999999% of bacteria and 99.999% of parasites removed. Its warranty is 3 years. The page we read does not name a testing standard for this model.

How to choose

• Match the filter to your household. At Ready.gov's one gallon per person per day, four people use about 15 L a day. By our arithmetic, a 1,500 L rating covers about 100 days of that, a 2,000 L rating about 130 days and a 1,000 L rating about 65 days. Real life depends on how dirty the water is.
• Rated lives are not comparable. Sawyer rates in gallons and up to 100,000, the others in liters at 1,000 to 2,000. Each maker sets its own rating, and none of them have been checked by us.
• Plan for cloudy water. The CDC says to strain it through a clean cloth or coffee filter, or let it settle, before treating.
• Plan the hanging point. A gravity filter needs something to hang from, such as a tree branch, a hook or a door frame.
• Keep it from freezing. Sawyer's help page for its Squeeze filter says a frozen filter is not covered by its warranty and should be replaced if you suspect it froze. Check your model's manual for the same rule.
• Price. Prices change often, so we do not print them here. Compare the current price on the seller's page.

Safety and limits

• Follow the maker's instructions. The figures here are the makers' claims, not our test results.
• Chemical contamination. None of these filters makes fuel- or chemical-contaminated water safe.
• No promise of protection. We compare published figures. We do not promise that any product will protect your health.

Questions people ask

Is a gravity filter better than a portable one?

It depends on the job. A gravity filter fills bags for several people without pumping or squeezing. A pocket filter weighs less. Both types face the same limit: they do not remove viruses.

Do gravity filters remove viruses?

None of the four product pages we read claims virus removal. The CDC says portable filters will not remove viruses, and recommends adding a disinfectant after filtering.

All four, side by side

Cells marked "to be verified" are figures we did not find on the maker's page. We leave them blank rather than guess.

Where the figures come from

• CDC: How to Make Water Safe in an Emergency
• Ready.gov: Water
• Platypus GravityWorks, product page
• Platypus QuickDraw 3L Gravity, product page
• Sawyer One Gallon Gravity, product page
• LifeStraw Peak Series Gravity 3L, product page and warranty page

Citing the CDC and Ready.gov does not mean they endorse this site. If a figure here is wrong, tell us. We fix it and note the change on the corrections page.