LifeStraw Flex Water Filter Review

If you spend a lot of time outdoors then water purification is going to be a consideration at some point. Some people are happy to carry several litres of regular tap water with them on an adventure, but if you’re already carrying 10-20lbs of camera equipment then this isn’t all that practical. I much prefer to travel with the Platypus flexible water bottles that I have talked about before, and then use a lightweight, pocketable water filter to top those up during the day.

My first stipulation for this kind of filter is that it should fit into the hip belt pocket of my backpacks, so that I can grab water from a stream without needing to take the pack off. I have been using the MSR Trailshot for a couple of years, but it’s not the fastest system in the world because you have to stop and crouch down while you pump it to filter the water from the stream. When I saw the new LifeStraw Flex I was immediately interested because you can simply scoop water quickly from a stream while you pass, and then do the actual filtration while you are walking along and drinking.

Filter Specifications

  • Removes 99.999999 % of bacteria
  • Removes 99.999 % of parasites
  • Reduces organic chemical matter (pesticides, herbicides, VOCs)
  • Exceeds NSF 53 standard for reduction of lead and other heavy metals
  • Exceeds NSF 42 standard for chlorine reduction
  • Exceeds US EPA drinking water standards for bacteria and parasites
  • Microbiological filter lasts up to 2,000 liters / 500 gallons
  • Carbon capsule lasts up to 100 liters / 25 gallons
  • Replaceable carbon capsule
  • Filter weight: 48 gr. / 1.7 oz
  • Removes 99.999% of microplastics

Note that like most small filters of this kind, the LifeStraw Flex filter isn’t going to remove viruses from the water. In order to get virus or protozoa removal you have to move up to something significantly larger and more complicated (or use water treatment drops). My choice in that category is the MSR Guardian.

Design and Usage

LifeStraw are well-known for their simple blue water filtration straw that has been around for many years. I have one of those as well, and it makes an excellent item to keep in an emergency preparedness kit. Recently LifeStraw started to sell several other products that use the same filtration technology, but offer a variety of different methods to actually do the filtration. The issue with their standard straw is that you either have to drink right from a stream by lying down on the ground, or you have to have a wide-mouth plastic bottle with you such as a Nelgene.

The LifeStraw Flex gets its name from its functional flexibility. You can use it it just like the standard LifeStraw if you want to, or you can screw it onto the top of a bottle, put it in-line in a hydration bladder hose, use it in the supplied soft bottle or add it into a gravity filtration system.

The soft bottle that comes with the LifeStraw Flex is probably the lightest option if that is your primary consideration, but it isn’t my favourite from a usability standpoint. The “straw” only reaches half way down the bottle, so once you have sucked up half of your water you have to contort the plastic bottle in all directions trying to get the remaining water to the bottom of the straw. This issue can be solved by cutting a 3-inch length of rubber hydration bladder hose and putting it on the bottom of the LifeStraw so that you are always sucking from the bottom of the bottle. Quite how LifeStraw themselves didn’t think of this solution is beyond me…

Perhaps my favourite way to use the LifeStraw Flex is to screw it onto the top of a Platypus SoftBottle though. The included rubber bottle that comes with the flex is only 650ml, but the SoftBottles give you many more options. With the straw screwed onto the top of the bottle, you can also give the bottle a squeeze as you suck though it which increases the flow rate to something much more satisfying. The size of the screw thread is pretty universal, so you could also use most standard plastic water bottles such as the popular-with-ultralight-hikers Smart Water bottles.

Another option is to pair the straw with a hydration bladder such as a CamelBak. You can either fit it to the end of the bladder hose as you see in the photo, or you can splice your hose in two and insert the filter into the middle of the line.

As you can see from the photo of the dismantled Flex straw, there’s also a carbon filter in the filter, as well as the hollow fibre filtration section. The carbon filter reduces bad tastes, odours and chlorine, and it’s removable and replaceable. In fact if you’re really counting the grams, you can just remove it and leave it at home. The carbon filter has no additional effect on the bacteria or parasite removal.

Filter Cleaning

Removable carbon filter

The LifeStraw Flex comes with a large syringe, and instructions to back-flush water through the filter with it at least 5 times before your first use. Make sure you do that, because the first couple of times I did it, the water came out extremely cloudy. Once you have it cleaned out though, I didn’t experience any weird tastes. I did note however, that they recommend cleaning your filter with the syringe quite often, in fact the manual says you should do it every day if you are using the filter constantly. I’m sure daily cleaning is overkill unless you are sucking up some really filthy water, but multi-day hikes might require you to carry the syringe to keep things flowing smoothly. All you have to do is draw water up through the filter with the syringe, and then push the syringe back down to blow the water back through the hollow fibre membrane. With reasonably regular maintenance, the LifeStraw Flex should be good for 2000 litres of clean water. When you think about it, that’s a heck of a lot of water! With the hand pump style of filter you could conceivably be filtering water in bulk at a campsite, 10 litres at a time. But with something small like this straw, most people are only going to be sucking a couple of litres of water a day through it. Good for 1000 day hikes then! Not sure I have done that many in my lifetime.

The biggest downside I can find for this filter is that the carbon filter is only rated to last for 100 litres, which isn’t as much as I would like. You don’t need this carbon filter for the overall filter to be effective, it’s mainly there to help with bad tastes in the water, but you’ll probably find yourself needing to buy some spares if you make solid use of this thing and care about the taste of the water. Replacement carbon filters are $12.50, so this will add considerably to the lifetime cost of the product.


LifeStraw have a real winner here as far as I’m concerned. I really like having a variety of options for different days of adventure. When I’m kayaking a big lake I have a bladder behind my seat so I can take the straw and fit it in-line on my bladder hose. On a long day of hiking I can pack it with a couple of Platypus SoftBottles, and on shorter ones I can use the included 650ml rubber bottle. I don’t think I would personally use it in a gravity filtration system, but the option is there if you don’t need water all that quickly. For $35 I think it’s a great purchase, and at only 48g (1.7oz), it’ll satisfy the through hikers and gram counters as well.

Photo of author

Dan Carr

Founder of Shutter Muse, full time photographer and creative educator. Dan lives in the Canadian Yukon, but his wanderlust often sends him in search of images all around the world to meet the needs of clients and readers alike.

Featured Posts

The Best All-In-One Tripod Head for Landscapes and Wildlife