Grayl Ultralight Water Filter Review

Simple and lightweight water filter for solo use

Water filters are becoming increasingly popular in the UK hiking and outdoors market, and what was once seen as a niche item for overseas travel and expeditions are now starting to be habitually carried in the UK by adventurers of all types.
The Grayl Ultralight purifier bottle is a bit of a hybrid between a filtration bottle and something that can be used to transfer that cleaned water to another container – something that dedicated water filter/purifier bottles often struggle with.
I have been trying it out since late summer, using it on wild camping trips and expeditions with clients in Snowdonia, the Lake District and Scotland.

grayl filter review uk
grayl ultralight filter review
Grayl ultralight filter

First Impressions

The Grayl travel purifier has been around for about 4 years now, and this is an update on the earlier model, which replaces the stainless steel outer of the original with BPA-free plastic and a few design tweaks.
It’s basically a water purifier/filter mated to a coffee press – the Grayl uses a piston action to push the filtration cartridge through the dirty water and forces clean water up through into the inner chamber.

You get three components – an outer semi-translucent plastic cup with a non-slip rubber base, an inner plastic cup with a filter cartridge at the base and a rubber seal at the top, and finally a lid with screw threads and a small loop for attaching to packs etc. My review sample weighs roughly 315g (weighing after I had begun to use it so there are few grams of water weight there).

The purifier has a capacity of 473ml at a time, and will process water at the rate of 2L per minute. That filtration cartridge will process 150L of water before it needs to be replaced and replacement cartridges seem to be readily available, costing about £25.00 per time.

The promises of this water purifier include protection “against pathogens (viruses, bacteria, and protozoa), particulates, chemicals and heavy metals“. It achieves this with a combination of “electroadsorption, ultra-powdered activated carbon and silver treated zeolites” in the filtration materials themselves.

Grayl ultra light filter
The replaceable filter unit
ultralight water filter
External fill-line marker
lightweight water filter
Non-slip base of outer

Field Testing

If you have a look at the embedded video below you will get an idea of how this filter works, but the process is easy enough to describe:

  1. Fill the outer cup from as clean a water source as you can find (in terms of sediment etc)
  2. Place the outer cup on a firm, level surface below knee height
  3. Insert the inner filter and unscrew the lid 1/4 turn (it won’t work with the lid on due to the internal pressure created)
  4. Firmly and constantly press down, using the weight of your upper body
  5. Once the inner section is fully inserted the inner section will be full of clean, purified water

That’s about it. Once you have your 473ml of purified water you can drink directly from the inner cup, or pour it into another container like a hydration bladder or another bottle. I found this quite useful for resupplying with water in the middle of the day, or for just topping up every time I passed a likely-looking stream or pond – including a pool of rainwater in a peaty, mossy bank somewhere on the side of the Caringorms.

It’s pretty tough, and I think it’s more likely that you will lose the lid or knock it into a moving river before you break the bottle – I would be interested to see if is actually bulletproof…

review water filter 2018
The Grayl Ultralight Filter

See the video below for more information and a demo of how it works

The Good Stuff and the Other Stuff

Simplicity, toughness and ease of use make this an attractive proposition for solo use. It promises a lot for a purifier at this price level – the complete treatment and removal of viruses, other pathogens and some chemicals and heavy metals is pretty much all I can ask of a device of this type for travel and expedition use.  I also like the shape, size and weight – I can just replace my drinks bottle with the Grayl if I am really worried about weight but want to carry a filter.

Normally when looking at water filters you are looking for the size of the ‘holes’ in the filter itself – how big a particle will it prevent from passing from the clean to the dirty side. The general rule of thumb is to look for  something with a filtration size of less than 0.1 micron to filter out viruses – but that doesn’t really apply to the Grayl. It makes use of a combination of electroadsoprtive media and activated carbon layers to remove the pathogens, particles and other contaminants. On the Grayl website they say:

The Purifier Cartridge uses a patented G3+™ Filtration Media– three filtration technologies in one for added protection: 1) A triple-charged mesh traps disease-causing germs while allowing water to flow quickly, 2) Activated natural carbon (made from coconut shells) attracts and traps many heavy metals, industrial chemicals, 3) An integrated anti-microbial agent suppresses the growth of mold, mildew and bacteria, keeping GRAYL fresh between uses.

This is starting to drift a little away from my professional experience (which has almost always been with either mechanical filters or chemical sterilisation) but as far as I can gather that mesh acts like a magnet for the biological contaminants and the carbon layer deals with everything else. This explains why there is a relatively short life for each cartridge – 150L, so a few months if used several times per day. At £25.00 per new cartridge that’s relatively expensive, but is possibly offset by the lower initial purchase price compared to similar filters.

All filters that bring the ‘dirty’ and ‘clean’ sides into close proximity need to be carefully managed as there isn’t much point in spending a lot of time and effort in purifying water if it’s just going to mingle with the unfiltered water around the edges of the bottle – this is true with the Grayl, and you need to be aware of how you use, store and drink from this bottle.

grayl filter test uk
On test in Gleann Mor
grayl filter review uk
Fits anywhere a water bottle will
grayl water filter
Filter unit
Grayl ultralight filter
Inside the filter unit
grayl filter review
Inner filter and outer sleeve

Final Thoughts

Water filters and purifiers are always difficult to test as an outdoor gear reviewer. I can test the overall design, compare it to others and see how it performs in the real world – basically, take it out and try to break it. But I don’t have a laboratory to go and test the filter itself – and if I did I wouldn’t have the first clue of what to look for. All I can go off is the information provided by the manufacturer and assume that they are being honest with what they promise that item can do.
So, as far as I can tell, the Grayl hasn’t let me down. The only problems I have experienced to date have been user error – not unscrewing the lid far enough or knocking the filter into the river and having to run after it.
I have been reasonably careful with where I collected the water from, avoiding anything with too much sediment or pre-filtering through thin fabric (like a Buff) to remove the particulates. In the video below you can some small ‘bits’ floating around in the untreated water before I press the filter down – that’s about as bad as it got.
I would need to invest in replacement filter cartridges soon as I am probably nearing my 150L limit for this one, but I am happy to do so as the combination of simplicity and performance is enough for me to choose this over some of my other filters.
It’s been living inside whatever bag I am using that week, and I will carry it on upcoming trips overseas to places where even tap water is slightly suspect.

If you can live with the slightly limited filter capacity then it’s worth taking a closer look at the Grayl Ultralight water purifier.

Grayl Ultralight Filter Specifications:

  • Capacity: 473ml (16 oz)
  • Fast and easy one press purification and filtration of water
  • Durable construction adapted to survive in any harsh conditions
  • Transparent design
  • Comes with an outer refill, inner press, interchangeable purifier cartridge
  • Loop cap for easy attachment to your backpack
  • Fast flow rate: 2 litres per minute
  • Replacement filter lasts for up to 300 uses (approx. 40 gal/150L)
  • Removes 99.99% of viruses (e.g. Rotavirus, Norovirus, Hepatitis A)
  • Removes 99.99% of bacteria (e.g. Salmonella, E.coli, Cholera, Shigella)
  • Removes 99.99% of protozoan cysts (e.g. Giardia, Cryptosporidium Amoebae)
  • Filters heavy metals (e.g. lead, arsenic)
  • Filters chemicals (e.g. chlorine, iodine)
  • Filters particulates (e.g. sediment, silt)
  • Active Technology: Electroabsorption (electroadhesion and ion exchange), ultra-powered activated carbon, and silver treated zeolites
  • The purifier is antimicrobial, chemical free and uses BPA free materials
  • NSF Filtration System Standards 42+53
  • US Patent 0729584
  • Dimensions: 9.62”x2.87” (24.5×7.30cm)
  • Weight: 309g
  • Material: Polypropylene #5, food-grade silicone, ABS food-grade plastic
  • Manufacturer: GRAYL
  • Manufacturer’s number: GR-004430
We went foraging with VICE and Max Halley
Examining a wild camp site - tracking and reading the ground

Grayl Ultralight Water Filter













  • Not much to break
  • Simple
  • Lightweight
  • Small


  • Limited filter life
  • Slow for group use
  • Limited capacity

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