Whether you’re carrying it in a canteen, a Nalgene bottle, or something else, it’s important to carry sufficient potable water with you. And that’s why today Nate is talking about the GravityWorks; a Platypus Water Filter for your travels.

“A pint’s a pound, the world around.”

This old rhyme has a few different meanings dating back to ye olde’ medieval Britain, but it also goes to illustrate how heavy water is. Sixteen fluid ounces of water isn’t much, but it sure feels like it when you have to carry it over distance. The ability to reduce the weight you have to carry in the field is important.

Think about it like this. One full gallon is 4 quarts, or 8 pints — that’s 8 glasses of beer (6 if you’re drinking the homebrew at Nancy’s Squat’n’Gobble).

If you’re at the pub, this would make for a great night, some terrible decisions and (quite likely) an awful hangover. But if you’re in the heat of the desert and active, a gallon won’t last you long. One gallon of water weights 8 pounds, and the more you carry on your person, the more you need it to stay hydrated. For those conducting combat operations in arid climates, it’s not uncommon to consume more than five gallons a day just to stay alive. Sometimes a grunt will carry more weight in water than he does in ammo, fearing the lack of resupply. For this reason, specialized units around the world have used water purifiers for years to cut down weight.

When operating in areas with abundant water sources such as streams, creeks, lakes and rivers, it’s almost a no brainer for a reconnaissance team or long-range patrol to bring a water filter system along and eliminate the need for water resupply. Filtered water greatly reduces the chances of illness in the field and a water filtering system allows you to keep potable water in your pack to a minimum. The lighter you are, the faster and easier you can move. Today we look at a viable option for field water treatment, the GravityWorks system from Platypus.

GravityWorks Water Filter Features

Platypus is a company that has specialized in hydration bladders for as long as we can remember, and we’ve used their products in the past with great success. The company was absorbed by Cascade Designs some time ago and their line continues to be produced under this banner. Their newest product is called the GravityWorks, and is an extremely light and portable means of filtering clean water. 

Platypus produces two variants of the GravityWorks:, a larger a 4.0 L system, and a smaller 2.0L system (we tested the smaller one for this article). The 2.0L system is incredibly light, weighting in at only 10.75 oz for the entire package. This weight is something to note, because that means the kit weights less than a single glass of water. The weight savings over packing bottled water are obvious, as you can refill your bottles or hydration bladders while on the move. 

The kit comes rolled up and stowed in its own mesh storage bag, and is small enough to fit into a cargo pocket. The system is very simple to use, as the user only needs to find a natural source of water, fill the included “dirty” reservoir, and let gravity do the rest. The two-liter reservoir is made from a pliable, durable material and features a zip-lock style closure at the top.

We filled it numerous times in various streams and creeks over the course of several camping trips by simply prying the top open and dunking it into the water. Once filled, the reservoir can be held or attached to a tree with the included hanging strap. The water filters down through a quick detach tube, and meets the inline filter. The dirty water is forced through the filter under its own weight, and removes bacteria and Protozoa, including Giardia, Cryptosporidium, E. coli, Salmonella and Cholera. For a more dirty water source, we would pre-filter debris and other contaminants out before filling the reservoir, to avoid clogging the filter. 

GravityWorks Water Filter Performance

In terms of use, filter performance is excellent. The flow rate is pretty quick, and on our timer we clocked a full one quart filled to the brim in 64 seconds. We also noticed that the cleaner the water, the better the flow rate. The line below the filter has an adjustable shutoff clamp, which serves a couple purposes. When initially using the filter, you need to let water flow through the system and then back-flush the filter to ensure proper function and to avoid cross contamination. This takes about four seconds, and is simple to remember. The filter is rated to process up to 175 liters of water. 

The only weak point of this system is the hollow fiber microfilter itself, which can be damaged from impact or abuse. The filter also must be stored dry over long periods of time, and safeguarded from the cold, or it will crack from the freezing water left inside. This should also be easy to avoid, as the filter element can be pulled from the kit and stowed inside your jacket. Keeping the small, light filter next to your body will help prevent freezing in cold climates, and ensure that it is not damaged as a result. 

In the field, we noticed that the purified water left the down line crystal clear, with no odor. The water also tasted superior to the local tap and well water, which was another perk. We used the GravityWorks to fill hydration packs, canteens and water bottles, and the system worked great with them all. The kit also comes with adapters to fit several sizes of popular commercial water bottles. We found these adapters to be kind of pointless, and would only pack them if we were expecting high winds to blow dust or dirt. Otherwise, the adapter just takes up room and adds weight to an otherwise small and light system. 

Overall, we really like this kit. The Platypus GravityWorks is a well thought out and relatively durable system. We like that they idiot-proofed it as much as possible, going as far as to print “DIRTY” on the dirty water reservoir, and by including a foolproof, waterproof pictogram instruction sheet sewn into the storage pouch to know where the clean reservoir is. You could be illiterate and still figure it out, which is good for any grunts out there.

The downside? There is no way to know when the filter is spent or damaged. You could jack up the filter, and have no idea you’re drinking contaminated water until it’s to late. This requires you to baby the filter element, and limit loaning it out to careless friends. The price for the system is a little steep as well, but that’s to be expected for a product made here in the states, particularly one that fills a specialty niche in the market. Having used the filter for a few months, it has now become a piece of mission essential gear in our day bags. Thanks to its simple design and good ole’ gravity, it sure as hell beats pumping or carrying clean water.