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The holey Grayl: Drinking cup filters water like a coffee press


July 15, 2013

The Grayl Water Filtration Cup

The Grayl Water Filtration Cup

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The Grayl Water Filtration Cup looks like a typical water bottle, but it's actually something quite different: a dual-walled cup that you can use to scoop water, filter out impurities and pathogens that threaten to make you sick, and drink out of, all in seconds. The cup is the latest alternative for filtering out intestine-shredding bacteria and viruses.

Outdoor enthusiasts have less and less reason to purchase and carry traditional standalone water filters and purifiers. Devices like the Camelbak All Clear Bottle, NDūR Survival Straw and Lifesaver bottle integrate water filter and purification systems directly into drinking vessels. Since you can use these to purify, drink and sometimes carry water, why bother with a standalone filter or UV purifier?

With such a broad market of devices already available, Grayl, a Seattle-based start-up formed last year, hasn't created a groundbreaking "holy grail," just a holey Grayl.

Grayl's system does have a different form factor than others out there. It is a double-walled container similar in design to a coffee press like the GSI Commuter Java Press. Instead of coffee grounds, it filters out pathogens and impurities. The mesh filter system is contained in the base of the inner cup, and all one has to do to filter water is fill the outer cup and push the inner cup down inside it. The water passes through the filter and is safe to drink once the inner cup is pressed fully down and filled with water. There's no sucking, pumping or UV-zapping.

Grayl's filtration technology is also a little different than some competitors. Its three-layer G3+ Filter uses an electroadsorption process that's created from a triple ion-charged mesh matrix laid over top its relatively large pores. This mesh serves as a sort of pathogen magnet, pulling bacteria, protozoa and viruses out of the water. Meanwhile, the carbon layer pulls out metals, chemicals, odors and flavors to give the water a clean taste, and the anti-microbial layer inhibits bacteria, mold, fungus and mildew growth between uses. The filter lasts for up to 300 uses.

"Grayl is different from other filters because the G3+ Filter and Purifier use 'electroadsorption' (aka 'ion-mesh' or electrostatic filtration), instead of 'mechanical filtration'," Grayl co-founder Travis Merrigan tells Gizmag. "Mechanical filters rely on tiny holes to keep bad stuff on the other side. Mechanical filters can't be made more effective by doubling the layers. Viruses will still squeeze through the holes. Conversely, Grayl relies on 'electroadsorption' - millions of tiny positive charges in a three-dimensional matrix. The water (and waterborne impurities) have to pass through a tortured path of this ion mesh, catching germs as they go."

The G3+ Filter is ample for areas where you don't have to be concerned with viruses, such as Grayl's North American home base. For areas where viruses are a concern, Grayl also offers the G3+ Purifier, which adds an additional layer for targeting all viruses.

"Electroadsorption efficiency (the amount of germs our filter takes out) increases both with the amount of ion mesh they pass through, and the amount of time spent in the mesh," Merrigan explains. "Viruses – being harder to catch than bacteria and protozoa – require more time and a more torturous path. So the purifier's double layer catches viruses; the filter catches less of them."

The company says that it takes about 15 seconds to push 15 oz (450 ml) of water through the filter and 20 seconds to push it through the purifier. The availability of the purifier is an advantage over some other systems, like the Vapur MicroFilter, which are not able to handle viruses because they are too small for traditional mechanical filtration.

While Grayl calls its product a cup, it's really more of a water bottle. It includes a lid with drinking hole that can be sealed by snapping the carry handle over it.

The stainless steel Water Filtration Cup is available for pre-order $69.95, which includes the filter. Additional filters are priced at $19.95 and purifiers at $39.95.


About the Author
C.C. Weiss Upon graduating college with a poli sci degree, Chris toiled in the political world for several years. Realizing he was better off making cynical comments from afar than actually getting involved in all that mess, he turned away from matters of government and news to cover the things that really matter: outdoor recreation, cool cars, technology, wild gadgets and all forms of other toys. He's happily following the wisdom of his father who told him that if you find something you love to do, it won't really be work. All articles by C.C. Weiss

I would like to see data re filter efficiency/max cycles/cleanable?/replacement cost..


my only concern here is that certain types of coliforms and cysts require contact with the filter for 30 seconds to effectively remove. how is this accomplished here?

Deborah Wright

Keeping one or two stowed away in your car or SUV at all times seems like a great idea, even if you've NEVER faced a circumstance of need for such things before. With something so small, it's easy to stay prepared.

@acorn - They gave that information in the article. Assume that they are NOT cleanable, will last for the stated 300 uses, and are replaceable at the prices given: filter $19.95, purifier $39.95.

@Deborah Wright - Easy. Filter -> pour into regular cup -> pour regular cup back into filter -> filter -> pour into regular cup -> pour filtered cup back into filter -> filter -> pour into regular cup -> repeat until you feel it's safe to drink. :)


The concept appears sound, but with pathogens present in the water sources for which filter capability is to be relied on for totally 'safe' potable water consumption, is not sufficiently reassuring!

Robert Gillis

Like the idea, but it still seems a bit elaborate compared to one of the filter straws etc, that are already (as mentioned) on the market. I would add that it is a lot easier to carry 6-10 (extra spares) thin straws in a backpack than 2-3 extra filters when usually space is at a premium. "Up to 300 uses" also sounds nice, but what happens to it sitting in the garage between hiking trips?

The Skud

As long as the filter can remove the viruses, that will be something great. However, most water filter say they can remove all viruses, but the viruses as small as .05 microns can still pass with little to no resistance, and people are unaware of this.

Adam Michaels

I'd still have the LIFESAVER because it filters down to 15 nanometres - 0.015 microns and filters everything sterile - so it cannot filter all viruses or bacteria - what about Polio being 0.025microns large? It wont filter that! I can list many many more....

Rachael Gordon
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