Water filters can be bulky and a bit faffy, but the Solo could hardly be smaller or simpler in principle. This tiny straw allows you to drink straight from water sources on the go, or can be paired with an old fizzy pop bottle or one of LifeStraw's existing soft bottles. It's a compact marvel, with obvious appeal to minimalists, but is it almost too short to use minus a pop bottle? It's certainly getting there. The small threaded end will only fit narrow diameter bottles, which rules out all of the many makes and models of non-disposable water carriers I own, with the exception of LifeStraw's own. The addition of a soft flask would make it practically perfect.

Weight and dimensions

This is a much smaller adaptation of LifeStraw's existing product, the Personal Filter Straw, and while it's not a huge deal lighter, 48g vs 65g (dry weight), it's only around half the length, at just 12.9cm. This makes it genuinely pocket sized in a way the older product isn't quite. I'd say 48g for a highly effective water filter is next to nothing, making this a brilliant little option for anyone watching their weight, from runners to backpackers.

What it filters

With a 0.2 micron pore size its microfilter membrane deals with 99.999999% of bacteria, 99.999% of parasites, and 99.999% of microplastics, so the Solo tackles most of the waterborne nasties you'll be likely to come up against in upland Britain.

If the water isn't running clear then the filter should be able to take out silt, sand, and cloudiness - though it may get clogged fairly quickly and require a backwash. Its effective temperature range of 0C - 60C should see you right in most situations, since you can't filter ice anyway.

It lasts up to 2000L, which is a lot of hillwalking or backpacking. At £29 that works out at just a 1.45 pence per litre, which is really excellent value.

Practicialities and limitations

The Solo comes only as a filter/straw. That's fine if your water sources are plentiful and you're able to get right down next to them to drink without getting wet and muddy. But if you're trying to use a trickle in a hollow, or a Pennine bog surrounded by peat slurry, then lying down to drink may not be the most viable option. Actually, I've found that even using small, clean lochans with strategically placed flat rocks to lie on (to avoid getting soaked by the grass) can be a neck-craning contortion, because the straw is so damn small. It is also remarkably difficult drinking your fill when lying flat out on a boulder - I tried my hardest for this review. To drink you really want to be upright.

That compact size is great when you're carrying it, but less so in use. And then there are those days when water sources are few and far between, meaning you have to carry some, and not just quaff as you go. That's when a simple straw hits a very basic limitation.

Bottle attachments

Fortunately its threaded end attaches to a standard 28mm disposable drinks bottle, so if you've bought some Lipton Ice Tea en route to the hills (other fizzy pops are available) then you can re-purpose the bottle for filter work rather than chucking it in a ditch (don't do that). Less fortunately, that size of thread does not match with many outdoor-oriented bottles or flasks. None of my soft running bottles fit it; neither Nalgene nor Sigg will marry up; and watch out for disposable mineral water bottles, because the necks of some of those are too wide as well. Try it with the one you intend to use before committing.

Perhaps LifeStraw could consider some kind of adapter to match with wider necks, since pairing it with a soft bottle is the most obvious combination. Alternatively, a long flexible hose attachment would solve the shortness issue of the straw.

As far as compatibility goes, the one soft bottle I know for sure it does fit is that supplied with LifeStraw's Collapsible Squeeze Bottle, which we reviewed last year. It's satisfyingly neat how it all matches up across the product range, though this info is not prominent on LifeStraw's website and I only recently found out! In fact the Solo is basically the filter unit from that established product, with the addition of a drinking spout and an end cap. But who wants to buy two very similar filters? Ideally I think they should make the bottle bit of the Collapsible Squeeze Bottle available separately, so that you can have the drinking straw benefit of the Solo in combination with the obvious advantage of a bottle, without having to purchase the pricier bit, the filter unit, twice. You can use the filter from the more expensive product as a straw, but since it lacks a protective end cap and a spout it's not quite as good as the Solo.

Common with all such filters flow rate is pretty slow - you're sipping, not gulping - and you have to suck quite hard when there's a bottle attached. Like a soft flask the pressure doesn't equalise, so your drinks bottle collapses as it empties. I guess if you were out on an extended journey then the multiple crunches of a cheap pop bottle might eventually lead to it splitting, though these things do seem pretty robust. You can of course use your disposable bottle to fill a Nalgene or similar, with a slow squeeze, though that would slightly negate the weight saving potential.

Maintenance

As with the LifeStraw filters I reviewed last year, keeping it in good condition is where the faff comes in. I will repeat what I wrote then to save you the spectacle of me trying to find a new way of saying it:

This isn't something to just store and forget about, it's a little bit particular since it wants to avoid drying out in order to maintain the properties of the filter, and to prevent the growth of mould and suchlike. If it's being stored for more than one month with no use then LifeStraw recommend filling it with a saline solution, while for storage over three months they say to clean it out with a diluted bleach solution (!) too.

Last year I said I would be unlikely to remember to do this, and I wasn't wrong. I haven't once filled my old filters with salt water, let alone used bleach (think I'd rather buy a new one than do that). They still seem to work OK.

The filter does however need to be flushed out regularly, to keep its tiny membrane unclogged: a 'backwash syringe' is included to do the job. Now this bit definitely is essential, something I discovered last year on an overnight ridge walk when silty tadpole nurseries were the only refreshment to be had, and my filter soon became so blocked I nearly burst my eardrums when sucking (I only slightly exaggerate). If out for more than a couple of nights I'd now always carry the syringe - an additional 30g or so.

Ethics and environment

LifeStraw are certified as a B-Corp. Primarily through their work in Kenya, for every LifeStraw product purchased a child in need receives safe drinking water for one year - see here.

Verdict

If cutting bulk and weight is important to you, and you want something for on the go, not sedentary camp use, then LifeStraw have nearly invented the perfect water filter here. What's the catch? Well I think it really needs a compatible soft flask to complete the system, since it's very short for easy use without a bottle, and it connects to too few bottle necks. The only one it definitely fits comes with a different (but near identical) LifeStraw filter, and that would mean buying two products. However for something this small and light I'm happy to work around the niggles, because the Solo really is brilliant.