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AutoFlow Gravity Filter

Fast, no-pump water filtration in an ultralight system.

Updated for 2017: The supreme ease of the AutoFlow Gravity Filter has converted many backcountry travelers to pump-free water filtration. Now, it offers the luxury of effortless water storage and filtration in a more compact, lightweight and streamlined system. Efficient hollow fiber technology filters up to 1.75 liters per minute, and quick and easy tool-free cleanings maintain high flow rates on extended expeditions. Choose the 4-liter system for groups and base camps. The 2-liter system is perfect for backpacking pairs.

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Updated for 2017: The supreme ease of the AutoFlow Gravity Filter has converted many backcountry travelers to pump-free water filtration. Now, it offers the luxury of effortless water storage and filtration in a more compact, lightweight and streamlined system. Efficient hollow fiber technology filters up to 1.75 liters per minute, and quick and easy tool-free cleanings maintain high flow rates on extended expeditions. Choose the 4-liter system for groups and base camps. The 2-liter system is perfect for backpacking pairs.
  • Tested: Meets NSF protocol P231 for removal of bacteria (99.9999%) and protozoa (99.9%) from beginning to end of filter life in “worst-case” water.
  • No Pumping: Lets gravity do the work so you don't have to.
  • Fast: Filters more than 1.75 liters per minute.
  • Lightweight: 2-liter system weighs only 300 g (10 oz.). 4-liter system weighs just 315 (11.1 oz.)
  • Field-Maintainable: Can be backflushed repeatedly without disassembly to regain flow rates.
  • Adaptable: Filter directly into most any bottle or reservoir with included Universal Bottle Adapter.
  • Assembled in the U.S.A. of U.S. and Imported Materials
Made in USA
4 LTR 2 LTR
Color No No
Style No No
Weight (Standard) 11.1 oz 10 oz
Weight (Metric) 315 g 300 g
Width (Standard) 11.3 in 8.5 in
Width (Metric) 28.7 cm 15.6 cm
Length (Standard) 20 in 15 in
Length (Metric) 50.8 cm 12.7 cm
Country of Origin Made in USA Made in USA

Documents and Instructions

Virtually all surface waters are contaminated with at least one of the three types of potentially disease-causing microorganisms: protozoa, bacteria, and viruses. A 1992 study found that 97% of U.S. rivers and lakes contain one or both of the protozoan parasites Giardia and cryptosporidia.
While it is true that you can drink directly from many water sources, it is critical to understand that each time you do, there is a chance of ingesting one of these bugs. Infection symptoms can range from an upset stomach to debilitating illness and, depending on where you are, can mean anything from a simple inconvenience to a life-threatening situation. Since microorganisms are impossible to see, taking the proper precautions with any water can help to ensure a safe trip.
Protozoa are the largest of the waterborne bugs measuring in the one-micron range. Giardia and cryptosporidia are the most infamous of the group. The infective cysts and oocysts of protozoa are extremely robust and can survive for months in a water source. They thrive in domestic and wild animals as well as humans. Cryptosporidia oocysts are known for their resistance to chemical treatment. Most disinfectants are ineffective, and the few that are require long dwell times to do the job.
Bacteria are an order of magnitude smaller than protozoa measuring in the 0.5 - 2 micron range. The most well-known bacteria are E. coli; others include Leptospira (which causes Leptospirosis), Campylobacter, Salmonella, and Shigella. Bacteria aren't as hearty, surviving in water only for weeks instead of months. However, unlike protozoa and viruses, which require a host to multiply, some bacteria can grow in water and so can be found in higher numbers than protozoa and viruses. Bacteria, like protozoa, are often carried by both animals and humans. Because of this, many water sources are contaminated with bacteria. Beware especially of sources near agricultural operations.
Viruses are the smallest type of pathogen, ranging between 0.02 - 0.3 microns. Waterborne viruses are very resilient and can survive for months. It is important to note that viruses are generally species-specific. In other words, those that infect animals do not infect humans and vice versa. Because of this, and the well-maintained sewage systems in developed countries, not as many water sources are contaminated with human viruses. However, in heavily traveled backcountry areas, viruses can be present where human waste is not disposed of properly. In developing countries with little or no sewage control, viruses are often widespread and purification in such countries should be standard procedure for all travelers.
First, it will usually take more than one organism to make you sick—around 10 for protozoa and viruses and 10 to 1,000,000 for bacteria depending on the species. The onset of symptoms can start anywhere from 10 hours to several weeks from the point of infection depending on the type and amount ingested, and constitution of the individual. Symptoms can range from nothing to diarrhea, abdominal cramps and pain, nausea, vomiting, muscle cramps, fever, fatigue, headache, chills, loss of appetite, and, in the case of hepatitis, dark urine and jaundice. Symptoms usually dissipate in a couple of days or weeks, again depending on the three elements above. Healthy adults will generally knock the illness without needing medical attention and without lasting effects. However, infants, young children, elderly, pregnant, and immune-compromised individuals are at higher risk of needing medical attention or having complications from an illness. Your location—a remote basecamp in Pakistan or a day hike close to home— will play a key role in the severity of your illness, should you become infected. For more information on diseases caused by specific pathogens, please visit www.cdc.gov.
A filter actually removes matter and microbes from the water while a "purifier" can employ a variety of methods to disinfect the water (such as UV or MIOX® or combination system like the MSR Sweetwater® purifier). A purifier must meet the EPA Guide Standard for Testing Microbiological Purifiers, which requires inactivation of all three classes of microbes: protozoa, bacteria and viruses. Filters in general claim to remove only protozoa and bacteria, making it adequate for most travel in developed countries. Some filters alone can qualify as a purifier, but since they are filtering to such a small pore size, they tend to clog quickly. Essentially the classification as a "purifier" means that the device must be capable of inactivating viruses, as well as protozoa and bacteria.
MSR microfilters remove protozoa and bacteria. The microfilters (MSR Sweetwater® and Miniworks®) that contain carbon can also reduce tastes, odors, some chemicals, pesticides, and herbicides.
Inactivate means to damage a microorganism sufficiently to render it harmless.
To decide whether you need a filter or a purifier, two important factors must be evaluated: water sources and susceptibility.

When evaluating water sources it is important to keep the following in mind: In general, protozoa and bacteria infect both animals and humans and are transmitted to water sources by animal and human waste. In contrast, waterborne viruses are species-specific and therefore transmitted to water sources by human waste alone. As a rule of thumb, remote areas with few people require (at least) filtration while popular areas with many human visitors require purification. If traveling in developing countries with poor sanitation, purification will be your safest choice.

Susceptibility is another good way to determine needs. If the treated water is to be consumed by infants or young children, elderly, or pregnant or immunocompromised individuals, then it is essential to use a purifier for the highest level of protection. Purification is also best for people who tend to get sick. If you rarely get sick and do not fit into any categories mentioned above, then filtration may be adequate depending on the water source.
Micron ratings aren't always the best way to gauge effectiveness. Test procedures for micron ratings vary so greatly that comparing them is misleading. In addition, micron ratings for filters do not tell you how the product will perform with actual bugs. There is an EPA Guide Standard for Testing Microbiological Purifiers, which describes how to test products to determine if they are removing or inactivating the proper number of pathogens in different types of water throughout the life of the device. When looking for a microfilter or purifier ask if the product has been tested according to the EPA Guide Standard and passed. For a microfilter, meeting the EPA Guide Standard means removing 99.9% of protozoa and removing 99.9999% of bacteria in all required water types. To be classified as a purifier, the device must meet the EPA Guide Standard for the removal of protozoa and bacteria as well as virus which must be inactivated to 99.99% in all required water types. All of the MSR filters and purifiers have passed the levels of inactivation required by the EPA Guide Standard with flying colors.
As a result of the September 11 attack and the following concerns about bioterrorism, we have received a number of inquiries regarding our microfilters' ability to protect against such threats. MSR microfilters will protect you from harmful microorganisms that are 0.2 microns or larger. The anthrax bacteria, for example, measures about 8 microns and would be removed by all MSR filters. Additionally, if a water reservoir were contaminated with a biological agent, it is unlikely that enough organisms could be added or would survive the treatment process of the water plant to provide an infectious dose at the tap. Our water supply is more likely to be compromised or cut off completely as a result of a natural disaster, such as an earthquake or hurricane, or by a general state of disorder following any kind of attack or natural disaster. By including a good water treatment device (and knowing how to use it) in your emergency kit, you will be prepared for most situations.
MSR filters will remove some tannins from the water you are filtering. Like other contaminants, they will clog your filter over time, requiring you to clean the cartridge. Tannins will react with disinfectants and can make treated water taste unpleasant. If possible, look for a clear water source to prolong the life of your filter and improve the taste of purified water.
MSR filters and purifiers provide microbiologically safe drinking water. The carbon in the filters and disinfectant of the purifiers will adsorb or react with some chemical contaminates such as herbicides, pesticides, and volatile organic compounds (VOCs). However, MSR filters or purifiers will not protect you from high chemical concentrations or heavy metal contamination. Do your best to avoid water sources such as mining tailing ponds or those near agricultural operations.
MSR filters and purifiers come with a limited warranty. Contact our Warranty and Repairs Department at 1-800-531-9531 if there are any problems with your filter or purifier and they will be happy to help with solutions.

What is California Proposition 65?
Proposition 65 is the Safe Drinking Water and Toxic Enforcement Act passed by voters in the State of California in 1986. The act was created to inform people about possible exposure to chemicals known by the State of California to cause cancer, birth defects and/or other reproductive harm.

What are the requirements of Proposition 65?
Proposition 65 requires that the Governor of California maintain and publish a list of harmful chemicals. The list is updated annually and includes chemicals that can be found in solvents, drugs, dyes, food additives, by-products of certain processes, pesticides, and tobacco products.

A chemical is listed if it has been classified as a reproductive toxicant or carcinogen by an "authoritative" organization on the subject. The U.S. Environmental Protection Agency, U.S. Food and Drug Administration, National Institute for Occupational Safety and Health, the National Toxicology Program, and the International Agency for Research on Cancer are considered authoritative for carcinogens. For reproductive toxicants, the authorities are the U.S. Environmental Protection Agency, U.S. Food and Drug Administration, National Institute for Occupational Safety and Health, and International Agency for Research on Cancer. Chemicals will also be listed if they are required to be labeled or identified as a carcinogen or as a reproductive toxicant by an agency of the state or federal government.

Why has MSR placed a Proposition 65 label on its products?
Any company with 10 or more employees operating or selling products within the State of California must comply with the requirements of Proposition 65. To comply, businesses are: (1) prohibited from knowingly discharging listed chemicals into sources of drinking water; and (2) required to provide a "clear and reasonable" warning before knowingly and intentionally exposing anyone to a listed chemical.

A Proposition 65 warning means that the business has evaluated the exposure and has concluded that it exceeds the "no significant risk level," or that the business is providing a warning based on the presence of a "listed" chemical without actually evaluating the exposure.

MSR is providing a warning based on our knowledge about the presence of one or more listed chemicals without attempting to evaluate the level of exposure. While using an MSR product, the exposure to a "listed" chemical may be well within the "no significant risk" range, but out of caution, we have placed the Proposition 65 warning labels on our products.

Are consumers who are using an MSR product with a Proposition 65 warning at risk?
The California government states: "The fact that a product bears a Proposition 65 warning does not mean by itself that the product is unsafe." The government also explained, "You could think of Proposition 65 more as a 'right to know' law than a pure product safety law."

A Proposition 65 warning means that the product contains one or more listed chemicals. By law, a warning is required unless the business proves that the exposure to the chemical poses "no significant risk." The "no significant risk" level for carcinogens is defined as the level which is calculated to result in not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime. Therefore, if you are exposed to the chemical in question at this level every day for 70 years, theoretically, it will increase your chances of getting cancer by no more than 1 case in 100,000 individuals so exposed.

The "no significant risk" level for reproductive toxicants is defined as the level of exposure which, even if multiplied by 1,000, will not produce birth defects or other reproductive harm. Therefore, the level of exposure is below the "no observable effect level," divided by 1,000. (The "no observable effect level" is the highest dose level which has not been associated with observable reproductive harm in humans or test animals.) For further information about California's Proposition 65, please visit http://oehha.ca.gov/prop65/background/p65plain.html

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Roberta
November 10, 2016
Yes, I would recommend this to a friend
Would not leave my gravity filter behind!
I bought my MSR filter in Leavenworth, Wa when it first came out probably 7 or 8 years ago. The first time I used it was going into the Enchantments. Instead of carrying a hydration bag in my pack I used my filter and bag. Unfortunately about 3/4 of the way up Asgaard Pass it sprung a leak! Some duct tape kept it functioning and filtering. Upon my way home I stopped in Leavenworth and they replaced the whole thing. Since it was replaced it has been back to the Enchantments several times and used on all of our hikes filtering water for as few of 2 of us ladies or 5. It has never let us down and saves so much time and energy. It was worth every penny.
kayakkjl
September 21, 2016
No, I would not recommend this to a friend
Effective, not Economical
Kayakers often filter multiple liters, 4 or more at a time; not like a hiker filling up a couple of water bottles from a clear mountain stream. By the end of our recent 10 day trip, our brand new filter was down to a trickle. The cost really adds up. I will probably try to not use it at all in tannined water anymore. By about 12-16 liters, even after backflushing every 4, it was taking a really long time. Backflushing took quite a bit of effort, squeezing the clean water reservoir like a bagpipe until I got a little trickle instead of intermittent drips; never got a decent flow back, from the start. At about 20 liters, we were taking water back to camp in the reservoir bag and letting it hang in camp until it got 4+ liters done, about an hour or more. It works great at filtering, but you might need to factor in time and carry a spare filter. Tannins seemed to be the problem in clogging up the works. We have used this system for 3 years on kayak trips, filtering about 8 liters every other day or so. Some people in our group using other (also MSR) filters had some similar issues. Backflushed it again when we got home; did a 2 liter test with TAP water, took 24 minutes!! counting the few minutes it took to get the bubbles out and get it flowing. This BRAND NEW filter has handled maybe 40 liters of water, max., and is almost dead. This is radically different than what is advertised. This is our third 2 week trip using the system, and our 3rd filter. Not sure its working out to be a really good investment for us, but very profitable for MSR and their high-priced replacement filters."
TheRavan
September 6, 2016
Yes, I would recommend this to a friend
No Pumping Required, but...
It is great that you don't have to pump as no one likes too. I have own two of the MiniWorks filters. The first time I used the unit it it flowed fast and i was impressed. But that fastest was the last time is flowed fast. I found for at best result you need to back flush pretty much every 6 to 7 liters not every 8. Even after a 2+ liter back flush, it still never flowed as fast as the first time. I don't use camel backs or carry any other bladders so to back flush which is a pain with just a normal water bottle as you have to squeeze the bottle. I also found that back flushing 1 liter is the minimum, 2 is better. So doing that math means that you filler 8, waste 2 on back flushing. If you happen to filler dirty water and you will you will back flush after 6 liters. Also back flushing will always take longer than filtering. This other issue with this unit is it is not the best for a quick stop on the trail to refill your water bottle, a hand pump is still the best option. So will I stop using this unit, no way as I hate pumping. I will just carry a small camelback bladder and just use it for back flushing. I am also going to carry two filters so I can filter and back flush at the same time and I have a spare. I like to use this unit with a 2.5 gallon plastic cube as it allows for hang and forget filtering and two fillings of the bag will fill up the cube. And remember to don't drop the filler or let it fresh. Also if you are in a group make sure someone else is carrying a hand pump filter.

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We know that in the backcountry, reliable gear is critical. That’s why MSR gear has always been engineered to the highest quality standards and rigorously tested before it reaches you. If your MSR gear is in need of repair, please contact our Seattle Repair Shop at 1-800-531-9531 and our technicians will work to find you a solution as quickly as possible. A majority of the time, MSR products can be repaired. If you are experiencing an issue with your product that you feel should be covered under the MSR Limited Warranty, please visit msrgear.com/warranty for more info.