Water Filter Straw for Hiking UK: What Happens When the Membrane Solutions S1 Leaves the Bug-Out Bag

Eighteen Reviewers Are Rating a Filter They Have Never Used

The listing carries 4.7 stars from 12,963 ratings. The 100 most recent reviews average 4.44, which is a gap worth naming rather than smoothing over. The breakdown of those 100: 78 at five stars, 8 at four, 3 at three, 2 at two and 9 at one. Ninety-nine of the 100 are verified purchases.

Now subtract the people who cannot possibly know. Eighteen of the 100 state they have not used the filter yet. They describe fast delivery, tidy packaging and a solid feel, then explain it has gone into an emergency box for a day they hope never comes. One reviewer puts it as well as anyone: the product is being saved, so there is nothing to report. Those are fair five stars, but they are five stars for a parcel, not for filtration.

The country mix matters too. Only 29 of the 100 are from the United Kingdom, with 46 from the United States, 12 from Germany and the rest split across Canada, France, Spain and Italy. The UK subset scores lower than the whole: 22 five stars, two fours, one two and four ones, averaging 4.28. Amazon also pools reviews across the pack sizes on this listing, so several reviewers are describing two, three or four straws bought together rather than the single unit.

None of that makes the S1 a bad buy. It does mean the recent average is softer than it looks. Add the 43 reviews that run to eight words or fewer, most of them a single word like "Good" or "Perfect", and the usable evidence sits in roughly 40 reviews rather than 100.

0.1 Microns, Five Stages and 57 Grams

The physical spec is the easy part. The S1 is 7.1 inches long, roughly 18cm, and 1 inch across, so about 2.5cm. It weighs 2 ounces, near enough 57g, which is less than a set of car keys and explains why so many buyers describe forgetting it is clipped to the pack.

Inside, the listing's cutaway diagram names five stages in order: a coarse filter screen, PP cotton, an activated carbon block, a second layer of PP cotton, then the hollow fibre ultrafiltration membrane. Pore size is 0.1 microns, which Membrane Solutions claims is 50% higher filtering accuracy than similar products on the market, and the quoted flow rate is 500ml a minute. Rated lifespan is 5,000 litres, or 1,320 gallons, which the brand translates as 10,000 half-litre bottles. The lifespan graphic tells you to replace the straw at that point rather than nurse it further.

On certification, the listing states the system is tested and certified by NSF International against NSF/ANSI standards 42, 372 and 401, covering chlorine reduction for taste and odour, lead-free materials, and microplastic and nominal particulate reduction at Class I. The bullets claim removal of 99.9999% of E. coli; the cutaway graphic quotes 99.99999% of total coliforms. Worth knowing what is absent as well: there is no virus claim anywhere on the listing, and Membrane Solutions states outright that the filter does not lower TDS, so mineral content and hardness come through untouched.

The carbon stage shows up in the reviews: several buyers mention taste, one noticing a clear difference in the water and another reporting no strange taste at all after filtering.

Six Buyers Could Not Get Water Through It

This is the failure that matters, and it is the largest single cluster in the set. Seven of the 100 most recent reviews report a filter that failed them, and six of those are about flow: one blocked after a couple of uses, one packed up after roughly a litre above 2,500 metres in the mountains, one of a pair bought together simply would not pass water, two could not draw anything at all, and one found the flow collapsed between the first use and the second.

The two most useful accounts sit at opposite ends. A UK buyer, J Watson, wrote that it was "Almost impossible to suck water through it, forcing you to suck so hard for half a mouthful you're left hyper-ventilating," adding that it would not gravity feed and the thread construction looked flimsy. Kelly Liming, who uses filters for backpacking, reported a different pattern: "The first time I used them they work great but the second time I used them they have poor flow. Even if it's only a few hours later."

Set that against the claimed 500ml a minute and there is clearly a spread in what buyers experience. Two more reviewers, in France and Germany, rated the filter positively while making the same point about flow: water will not run through on gravity alone, and the stream from the outlet is thin rather than forceful. The seventh failure is Yahya Imran, a UK buyer who had no trouble with flow and every trouble with the result, saying water from a stream came through "murky and frothy".

Seven in 100 is not a recall-level defect rate at this end of the market, but it is high enough that a single straw is a poor plan for a trip where water is the only variable you cannot walk away from.

The Rinse With Clean Water Instruction That Annoys People

The single most upvoted review in the 100, with 43 helpful votes, is a one-star from a UK buyer named Henry, and it is not about build quality at all. He quotes the instructions back: "when dry wash with drinking water.. don't use with salt, polluted or contaminated water", then asks the obvious question. "Is this not supposed to be for emergencies where you dont have clean water?"

He is not alone. Three of the 100 raise the same objection, and two of the four UK one-star reviews are about this instruction rather than any fault with the product. A Millward called it "Fairly useless for emergency use to clean dirty water as they have to be rinsed in clean tap water or bottled water before use". A four-star reviewer reached the practical conclusion instead of the angry one, pointing out that if you must soak before use and backwash with clean water afterwards, the sensible move is to prime and use the filter at home first, before it ever goes near a bug-out bag.

That is the right read. A dry hollow fibre straw needs wetting to draw properly, and the people reporting a filter that will not pass water are, in at least some cases, describing a straw taken straight out of a sealed bag and dunked in a stream. It is a design compromise the packaging handles badly, and Membrane Solutions could fix a chunk of its one-star reviews with a clearer line on the box.

Practical version for a UK buyer: open it the day it arrives, run half a litre of tap water through it, backwash it, dry it, then pack it. An unprimed filter is one you are gambling on.

Backwashing Is the Entire Maintenance Plan

Both ends of the S1 unscrew, and that is deliberate. The listing's backwash graphic labels the mouthpiece as the clean water outlet and the opposite end as a threaded water inlet cap. To backflush, you screw a bottle of clean water onto the outlet end and squeeze it backwards through the membrane, pushing the trapped silt back out the way it came. Done regularly, that is what carries the filter towards its 5,000 litre rating instead of clogging at ten.

The method has a critic in the review set. Taylor, one of the one-star reviewers, objects that other personal filters ship with a large syringe for backflushing and this one does not, calling the opening a "half straw" and saying a syringe cannot be used on it. That is a fair description of the trade-off: you get a lighter, cheaper package and you supply your own squeeze bottle. It is not the same as having no cleaning route, but if your last filter came with a syringe you will notice the difference.

What the reviews suggest, taken together with the flow failures, is that backwashing has to be a habit rather than a rescue attempt. The backpacker whose flow collapsed a few hours after the first use is the case that makes the point. Backwash while it is still running well, at the end of each session, and carry a spare bottle of filtered water specifically for the job. That single habit separates most of the happy reports from most of the unhappy ones.

Screw It to a Bottle, Stop Drinking From the Stream

The buyers who rate this filter highest almost never use it as a straw. They thread it onto something. One US reviewer flags the detail that makes it work: "it is threaded for 28mm bottles (such as the smart water bottle)", which covers a huge share of supermarket drinks bottles and most soft flasks. A Canadian buyer on a self-supported hike described screwing it onto a bidon to move water from one container to another, which is a far more comfortable job than kneeling at a stream.

The listing supports four setups: gravity, squeeze, storage and direct drinking. The gravity option is the one to treat with suspicion, because it is also the one reviewers push back on hardest. A French buyer noted water will not run through on gravity as advertised and that you need to connect a bottle and squeeze it, and a German reviewer measuring his Norway trip said relatively little water comes through per minute, so he carried a separate pump filter for the evening's bulk water and kept the straw for small amounts on the move.

Take that split as a buying instruction. If you want litres waiting at camp rather than mouthfuls at the water's edge, buy the SimPure Gravity Camping Water Filter instead, which hangs off a branch with a 3L bag and does the work while you pitch, and which we covered in our gravity water filter review. For one walker topping up a bottle, the S1 is the lighter and cheaper answer by a distance.

The durability reports back that up. Luke B, whose review picked up 9 helpful votes, took his "through the Scottish Highlands into the land of the Welsh" and reported "Really good build quality even with many falls and drops. Its survived and still works to this day." Another UK buyer uses them while teaching young people to find water outdoors, and rates the handling in bad weather.

Our Score, and the Two Groups Who Should Skip It

We score the Membrane Solutions S1 at 4.1 out of 5, below the 4.7 lifetime badge and below the 4.44 average of the 100 recent reviews we read. The deductions are specific: seven of those 100 reported the filter failing them and six of those were flow failures, three took issue with the pre-rinse instruction, and 18 of the reviews propping up the average come from people who say they have never used it. The UK slice of the set averages 4.28, which is closer to our number than the headline is.

Two groups should look elsewhere. The first is anyone filtering for more than one person or wanting bulk water at camp: the flow is a trickle by design and a gravity system does that job properly. The second is anyone buying this as sealed insurance to shove in a bag and forget for five years. The pre-rinse and backwash workflow means the S1 rewards an owner who primes it, tests it and keeps it dry, and punishes one who expects it to work perfectly out of a box in a crisis.

Everyone else is well served. For a solo hiker, a DofE expedition, a travel kit, a car glove box or a day walk in the Peaks where you would rather carry 57g than two extra litres, it is a lot of capability for very little weight, with a real NSF certification behind it and a 5,000 litre rating if you look after it. Prime it this week, backwash it after every use, and carry a second one if the trip depends on water with no backup.