Over the years I’ve spent backpacking through the nearby Uwharries and Appalachian Mountains I’ve used a number of methods to insure the purity of my drinking water. A couple of things I have decided. First I don’t like chemicals. Sure they are lightweight but I don’t like the taste. Why in this world would anyone hike to a clear running mountain stream and add chlorine to it? It just ruins the taste. And have you read the wait times on the label? I’m just too impatient to wait thirty minutes to kill what may (or may not) be lurking in my next thirst quenching drink. By the way that does not include the four hours for cryptosporidia.

As for water filters I have problems with them as well. After a long hike who wants to spend time hand pumping water? Certainly not me. All I want to do is drink the water. As for weight the lighter the pump the more pumping is required. Until recently I carried a Kaytadyn Hiker. It delivers about 1 liter a minute. Their new lighter weight model only supplies a ½ liter a minute to safe a whole 3 ounces. That’s a lot of pumping when you are hot and tired and just need to relax.

A few weeks ago I came across a possible solution. Kaytadyn markets a gravity filter. A Hiker filter cartridge is mounted in a dry sack. Water is collected in the sack and filtered water is deliverer by a tube for drinking. However just as I was about to order one to try on my next trip I spotted a drawback. It weighs 15.5 ounces. But I did like the concept. I started playing around with some materials and came up with a homemade version that weighs about 8 ounces. While it is still heavier than chemicals it is as light as their lightest filter. I decided to try it out on a week-long trip in the Smokies. Not only did it perform well, it supplied three hikers with all the water we wanted the entire week. The best part is while others were pumping or adding chemicals we were setting back enjoying the scenery and cool mountain water. We were also the object of a lot of attention with questions about our water filter system.

So here is how to make a gravity filter from readily available parts. First the materials.

8 liter waterproof stuff sack* WalMart $ 9.98
Hiker Pro filter cartridge REI 34.95
32 ounce Nalgene bottle** REI 5.95
48” of ¼” tubing Lowes .89
Total materials $51.77

*three bags in the package
**high-density polyethylene bottle

The mouth of the Nalgene bottle is a perfect fit for the filter cartridge. I also added a quick connect adapter to the tubing to attach to my hydration bladder. CamelBak markets a set for $7.00.

Putting this together is really easy. If you can handle a utility knife without cutting yourself you have all the skills you need. Start by cutting the water bottle below the plastic ring at the screw threads. Make the cuts as smooth as possible to avoid damaging the bag over time. You can smooth this even more with a piece of sandpaper I’ll refer to this part as the bottle neck.



The next step is to cut the water bottle cap to allow the filter to fit through. All that is really needed are the screw threads so don’t be afraid to cut. Use medium grit sandpaper to smooth the inside of the cap ring and to insure the filter cartridge will pass through the cap.



Screw the cap ring onto the water bottle neck and check if the filter cartridge will slide in. The fit should be tight. Once you have the hole the correct size, place the bottle neck inside the water bag with the threads centered on the bottom of the sack. The position is not critical. Now screw the cap ring on the bottle neck over the bag from the outside.



Cut away the cloth inside the ring. Some cloth around the edge may be left.



Now spread a small amount of the lubricant that came with the filter around the black O-ring. Slide the filter through the bottom of the bag so that the discharge is on the outside of the bag. Attach the tubing to the filter and fill the bag with water. You will have to prime the filter the first time you use it. Be careful not to suck the carbon into you mouth. It will not hurt you but it’s not a pleasant experience. Allow at least a liter of water to pass through the filter prior to the first use.

As I mentioned earlier I connect the filter to my water bladder to refill it. The higher the filter is above the bladder the faster it will fill. The time to fill the 70 ounce bladder varies but usually it is full in 2-3 minutes. Of course since I’m not pumping I really don’t care if it fills at a rate of less than one liter a minute.



Maintenance on the filter is easy. If the filter clogs in the field, Kaytadyn has a pre-filter sleeve on the cartridge that can be removed and cleaned. Since this is on the pre-filtered side it can be cleaned in untreated water. The filter cartridge itself can be rinsed in untreated water to help clean it. Just keep the discharge opening covered to prevent contamination. Kaytadyn claims about 200 gallons from one filter depending on the water. I never got that much from a pump but without the pressure of the pump I am hoping to come close.

After a trip I remove the cartridge from the bag and wash the bag with clean water. The tubing and cartridge are washed in a 10% bleach solution and allowed to sit in the mixture about 30 minutes. I figure that should kill most anything trapped in the filter. I then allow it to dry over-night prior to storage. Before I use the filter on the next trip I run about a liter of water through the unit to flush out the taste of bleach. This is the same procedure I used for several years with the Hiker pump.

While hiking I keep the hose in a snack size zip lock bag. This helps avoid any contamination. I use the smallest stuff sack that came in the set of three to hold the filter/bag, cleaning sponge and baggy with tubing. It is stored in the top of my pack so I can get to it easily.

After I built mine I discovered you can buy a similar filter from ULA. It’s called the Amigo Pro. With shipping it cost about the same, but if you have an old Nalgene laying around and a spare silnylon sack, build your own.

For prevention of cross contamination, you may want to use the technique of looping the output hose as in the attached photo.

Great job with the DIY project.

Cross contamination is not really a problem during fitration. It is only during storage since the hose and water bag are stored together. By placing the hose in a snack size baggie this should prevent the problem.

I really don't worry about it too much since I am very picky about my water source. An article earlier this year titled Sipping the Waters: Techniques for Selecting Untreated Backcountry Water for Drinking
by Michael von Gortler, MD is a great guide to choosing water sources. I pretty much follow the suggestions and still filter to stay on the safe side. There have been a few sources I have decided to trust but it was water running out of cracks in rocks where there were no obvious signs of large mammals.

Thanks for the feedback!

Edited by CaptainJac on 08/09/2007 14:49:57 MDT.

I guess I should have called it the "hose" instead of the "output hose", as there is really only one hose in a gravity feed system (from the unfiltered container to the final container).

How do you put water into the green stuff sack?

After attaching the hose to the filter I dip the bag into the water source. Just keep the hose out of the water as much as possible. I usually hold the end of the hose up with the top of the bag and that way water does not start to flow until I have hung the bag.

I dip the open end of the bag into the water source while holding the hose out of the water. As long as the discharge end of the hose stays above the water level no water passes through the filter. If you connect the top of the bag you can use it as a handle to carry water back to where you are camping/cooking. Then connect to your water bottle or bladder and shortly you will have cool clean water to drink.

your setup looks really nice. I had played with the same idea of a dry bag but desided to go with the ray way or ULA style.

The one pictured below weighs in at 6oz and I use my bear bag line to hang it. To save even more weight I've used the hose from my blader As Bill does but I don't always have it in the summer. I've found this setup works well.

I did some searching on this site and found Bills set up however no one had sourced the nylon fittings. I did some searching on the web and found them in a few places.

Joe F

http://www.usplastic.com/catalog/category.asp?catalog%5Fname=USPlastic&category%5Fname=18309&Page=1

Edited by need2boat on 08/10/2007 10:21:44 MDT.

We're in the same ballpark on weight. The weight I quoted was after weting the filter. It is almost 2 ounces lighter out of the package.

Which fittings are you using to connect the filter?

I use a Hiker Pro filter cartridge but it's been cut down quite a bit. all the threds and extra weight are cut off as I don't need them.

I'm not really a hudge weight guy as I could use to drop a few pounds over any of my gear. ;-)

I used the Cuben becasue I had it. My weight is with a wet filter as well. I weighed it right after i took it down.

The biggest savings for me was using the bear bag line to hang it, using the blader hose right to it, and cutting the filter down saved about an ounce. I could have dropped a few more if I didn't use the metal rings and made the over all pattern a bit smaller. I used 24" round but I thing bill and a few others have used 21"

Joe F.

Here's a picture of what my filter looks like after it's been cut down.

Joe F

Just FYI, Gardenville's project #3 from Sept 2005 on the following site does the same thing, modifying a ULA Amigo to use Cuben and cutting excess plastic off the filter itself:
http://ultraliteskunkworks.blogspot.com/2005/09/cuben-connection.html

I have a ULA Amigo, and after I saw the above reference I cut off the excess plastic on mine too, using my bandsaw; pretty easy, saved a little weight, not a huge difference but somehow emotionally ... satisfying.


Brian Lewis

The final weight of my modified Hiker Pro Water filter was 1.9 ounces. My complete Gravity Water Filter weight was 5.61 ounces.

Pizzaman,

Thank you for the "step-by-step".

Todd

Where in Walmart are the stuffsacks?

The stuff sacks are in the camping (sports) department. All WalMarts do not have them. There are 3 store near my home and only one has them in stock. All three are Super WalMarts. Go figure!

As suggested by a few of the messages I cut away the threads on the filter (except for the last one needed to prevent it from pushing through the pastic ring on the bag). It lowered the weight about a 1/2 ounce.

Bill-

Do you have any pictures of the finished modified Hiker Pro Water filter? I got mine down to 2.8 with the prefilter mesh it came with. Did you cut away the filter on both ends.

Joe F.

Thank you.

Joe

I only cut away at the end with the threads. If you look at one of the earlier messages it will show all the threads gone. I only cut to the last thread leaving a lip to stop the filter from going all the way through the mounting ring on the bag.

The setup the Amigo Pro and RayWay use puts the entire filter inside the bag so that none of the threads are needed. This is a good design just not the one I picked.

Edited by CaptainJac on 08/13/2007 11:09:41 MDT.

Hi Joe, (or anyone else that may be in the know)

Which fittings and gasket specifically did you buy at

http://www.usplastic.com/catalog/category.asp?catalog%5Fname=USPlastic&category%5Fname=18309&Page=1

And can anyone post some better pics of these parts seperated. Do you need to glue anything together?

Thanks,
Tony

Hi Bill, (or anyone who may know)

Can you tell me if the parts to your gravity feed filter look like the pics below?


Can you describe or post a picture of the gasket that goes between them and how you put it together?

Thank you,

Tony

This is pretty cool. I think I may give it a try.

What holds the filter in place? I read the directions but when you put the filter in does it use friction to stay or do you put it in then screw the top on? Sorry for the noob question

Tommy

Tommy,

The inside of the neck of the Nalgene bottle is the perfect size to hold the filter in place. Cut the hole in the cap so it is tight when you press the filter into it. That will prevent leaks. The filter slips in after the bag is fully assembled. Once you put it together the filter will pop in and out for easy replacement.

I've been using the one I made back in the spring and it hasn't missed a lick. I have started carrying an extra plastic baggie to dip water out of streams to make sure there is no cross contamination. On the AT the set up works great at any of the springs with water pipes extended out. I'm finding that the filter does not get as dirty since dirt is not forced into it by the pump.

If you have any more questions PM me and I'll post them here.

Edited by CaptainJac on 11/21/2007 14:29:37 MST.

Here are a few pictures of another DIY gravity filter bag.







Attach tubing to the spigot and then to an in-line filter. You can put some prefilter material inside the cap as well.
This can be made lighter by using a Platypus top instead of the Nalgene ATB top and by using less silnylon (this one hold 2-1/2 gallons).

Edited by Lancem on 03/12/2011 22:47:20 MST.

I think I have about $30 in this thing.
Just used off the shelf stuff.



AntiGravity Gear silnylon 1 gal water bag. Appears to be just like my Brawny water bag.
Aquamira Frontier Pro disposable water filter. BPL has 'em.



Marked the bottom of bag and melted a hole about the size of a dime I guess, with a red-hot pocket screwdriver.
Unscrewed the part that holds the pre-filter on the Frontier Pro and screwed it down tight on the bag. Put a 3/4" piece of hose on the filter's nipple (inside the bag) to create a silt settling reservoir. This leaves about an inch or so of water in the bag. Used the small straw/hose piece that came with the filter because it has to fit inside the nipple on the filter, and the 1/4" hose I had was a little small to fit well. Put a cut-down 1/4" hose coupler nipple on the end so I could plug it into my Platypus drinking hose.
Filled up my 2l platy while still in the pack, fairly quickly.


The manufacturer says the filter is only good for 50 gals, but it worked well and it had already been on one weekend trip.

This is a shot of bundle size and weight. Note: this is still wet.

Edited by Thangfish on 04/19/2008 10:34:51 MDT.

Got to try this filter out this weekend.
No problems.
Here it is in use at the Thomas Knob shelter water source at Mt. Rogers. Several other people are squatting and pumping, downhill just out of the shot while they watched me take this picture, and have a handful of dried fruit.



Here I have filled my 2 reservoirs, while my friend watches his get partially filled with the leftovers.



Can't wait for the Platypus gravity filter, inline replacement cartridge to arrive. Should have a much longer life span and much higher flow rate for about the same weight!

Edited by Thangfish on 05/06/2008 17:11:28 MDT.

This is awesome! How did I miss this? I've got to make one of these, thanks for the post!

All of the posts on this subject have been very inspiring. Let me add one improvement. I recreated the equivalent of this project using only the filter, the Walmart bag set and a few dollars in extra home supply parts. In doing so, I eliminated the need to make any modifications to the filter cartridge, so if you take this approach, you don't have to grind off any threads since this method uses the Katadyne filter without modification.

I discovered that pieces from a common schedule 40 2" PVC pipe and slip end cap, sliced into a ring set, are ideally sized to replace the Nalgene water bottle parts. In practice, you push the end cap onto the pipe and then slice the common area to make a ring set. I made a set approximately 1/4 inch in thickness. You then place the inner ring on a flat surface, turn the bag inside out and position it over the inner ring, and then squeeze down the outer ring to clamp the bag in between the two rings. You then carefully cut the nylon bag out to make room for the filter and press fit the filter into the inner ring opening. Walla, you're done!

Some other hints on this method. While the outer ring slips over the inner ring very snugly by itself, it will be really snug with the nylon bag material and the filter inserted. So I first rough sanded the inside and outside diameter of the pipe to help this fit a little. If you can, plan on never taking the rings apart after you cut the bag material. It becomes difficult to line up the material the same way once they are separated. Also I used a miter saw to make rings with uniform, clean edges, although I don't see why it wouldn't work if you hand sawed the rings. To keep it safe, make sure you are cutting through both the end cap and the pipe on each cut and have enough length of end pipe to steady the assembly while cutting.

Once the bag is clamped, its a snug fit to insert the filter, which is actually a good thing. If you remove the O ring, you should be able to insert the filter all the way up to the threads and make a very tight seal that won't easily come loose. Finally, I loosely placed the filter in the hole, and then rested the assembly in the open jaws of a bench vise so that I could 'knock' the filter down using a wooden block and some gentle taps.

The whole assembly weighs 7 oz dry (9 oz damp) and filters 2 liters in 7 minutes. Here are some photos of the finished assembly. Note I slipped the O ring back on after assembly just for the sake of storing it on the filter in case I ever need the original back.

Edited by glennt on 05/30/2010 09:48:45 MDT.

This system is Easy too and much lighter!


Brass screen filter ways 0.5oz and is used before liquid Aquamira.

Edited by Creachen on 05/30/2010 10:33:11 MDT.

Good looking design and nice weight, too!

The only potential problem I have found with gravity filters that have the filter in the collection bag, is lack of pressure for some filter cartridges.

The cartridges that have a slow flow rate, need the filter near the bottom of the tube to take advantage of the pressure from the long column of water.

But, then again, one of the nice things about a gravity filter is that you get to stop and smell the roses, while the filter is working :-)

[q] The only potential problem I have found with gravity filters that have the filter in the collection bag, is lack of pressure for some filter cartridges. [/q]

I've been using the Katadyn hiker base camp gravity filter for a few years and have never had an issue with it needing pressure.

It looks like it's time for me to lighten up though and convert it to use one of these walmart bags. I've got the walmart bag and the 2" pvc, just need an end cap and I'm good to go.

Edit: My Base camp filter came with a plug for the filter so I take the hose off and plug in when dipping it in the water to fill it. I never worry about cross contamination that way. I then take it back to camp and hook up the hose.

Edited by jeepcachr on 06/03/2010 09:42:52 MDT.

I have made a filter just like the first one shown in this thread and I too have never had an issue with lack of pressure. The Katadyn filters work wonders for me.

I didn't mean to imply that this isn't a great setup. The Katadin and many other filters will function swell in this mode.

I was just trying to make the point that the filter should match the setup. I've used Sawyer's virus filter and it needs all the help it can get from gravity due to it's tiny pore size, which nearly filters out water molecules :-)

As far as I'm concerned, gravity filters are the only way to go. I've pumped and I've Steripened and I've waited 4 hours for chemicals to kill giardia. Nothing beats hanging a bag, finding some other task to do and coming back to purified water.

That said, I don't believe in doing half a job. Just filtering will leave viruses in the water. Chlorine will kill the viruses almost instantly, but it leaves a bad taste. What to do? I follow my Sawyer bacterial filter with a Katadyn charcoal filter. The activated charcoal removes the chlorine I added to kill viruses leaving great tasting purified water. The filter setup is pictured below. One end screws onto a platypus bag holding the dirty water. The other snaps into my Nalgene hydration bladder. The right angle under the charcoal filter is a valve. Total weight including platypus bag is 9.2 oz.

Edited by herman666 on 06/04/2010 12:18:02 MDT.

This thread inspired me to try my hand at making something like this. I used silnylon cut into a 32" diameter circle. I used the cap off a 16 ounce cheapo water bottle and a 1/4"X1/8" nylon hose fitting. I used silicone to seal the inside. It's not done yet but I plan to finish it tomorrow. Would have preferred cuben but I figured I would use what I had on hand for now. I plan to use an inline filter with 1/4" hose barbs with this water bag.

I already had a katadyn base camp, a old nalgene, and the walmart water proof bag. I converted to the walmart bag and saved 4 onces plus it packs smaller. I only gave up a small amount of water capacity by going to the smaller bag but its still larger than what I will typically need. I thought about using the medium or small bag walmart bag but it wasn't worth the fraction of an once to go smaller.

I am not a gram weenie. I consider myself a lightweight guy not an ultralight. I'm very happy with this mod.

If this basic set-up has been posted before my apologies.

Thanks and all credit to hammock forums Angry Sparrow: a truly creative outdoorsman.

http://www.hammockforums.net/forum/showpost.php?p=174954&postcount=19

The filter shown weighs 5 oz with the zing-it hanger( filter/bag/fittings/hanger only.... no tubing, no 2 liter platypus........ plus a wet filter weighs more for quite some time ) and can be used as a hydration system with no extra bag(drink through the filter) It could probably likely be cut to 4oz by trimming the non-filtration parts off the micro-filter and using one of Lawson/mountainfitter cuben dry bags.

The bag shown is a 4 liter Sea to Summit from REI















Apologies for the sideways shots. Fill it, hang it and forget it.

PPS: Tony; the link above has the fittings source and part #'s and them appear to be those. haha

Joe: nice job on trimming the filter! using your weight for a trimmed filter yeilds a weight for this set-up of 3.4 oz. The dry bag closure has a rigid strip around the bag rim @ 1" wide and buckles which undoubtedly "wastes" at least the .4 and likely more.

I've been encouraging Lawson at Mountainfitter to design a cuben bag for just this purpose. Come-on Lawson! A 200 gallon 3 oz smooth flowing.... not so inclined to plug-up ( hint hint frontier-pro), micro-filter gravity system/ hydration system.

Edited by obxcola on 06/10/2010 12:02:57 MDT.

Lightweight filters do seem to have come a long way. I use one from DrinkSafe Systems.

They have ready-made gravity bag systems, too.

I know; this sounds like a commercial plug, but I have no connection with them other than as a customer.

ps. I know it's not MYOG, but it's a bit hard to MYOG viral filters...

Edited by captain_paranoia on 06/10/2010 12:39:22 MDT.

Thanks, Cola, for the great pictures and the link to hammockforums for the supplies! I need to order tubing and will be making my own as soon as it arrives!

You're welcome Mary! I'd suggest you order about 3 or 4 of each part since the shipping ends up being one of the biggest expenses.

BTW The plastic end caps for closet maid shelving work great as a plug for the outlet fitting. Allows you to fill the bag, carry it around etc without the hose attached
(and held up high to keep it from draining!)

Ordered a Cuben Fiber CTF3 Rolltop Drybags @ $15.95
size: 8"x12 from mountainfitter.Quoted as 4 liters. Wish I had a bandsaw like Joe. Guess I'll carefully try the table saw. 3oz or bust!

the table saw doesn't seem like a good idea. it would only take a minute to do with a hand saw or hack saw.

Tim problem is the depth of the cut needs to be just right, and those microfilter casings are made of tough plastic.

I don't know I guess I'm afraid I might slip doing it by hand.

The first time i read a report about trimming off the excess on hammock forums the guy used a dremel. That's a hand tool but a fast blade is also easier to control. I guess a lttle reticence about which way to proceed is why I haven't trimmed the thing yet.

Any good ideas about trimming the casing on a microfilter out there?

I just received the 4 liter dry-bag from Mountainfitter. The black bag! Appears very well made and wicked light at .5 ounce. Just about a perfect size and shape for a filter/hydration bag.

if I can trim the micro-filter to Bill F's weight of 1.9 oz that would yield a sub 3 oz gravity filter with a 200 gallon life that is easily modified on the fly for hydration and is minally prone to clogging. Dry-Bags with a semi-rigid rim are really easy to fill as well.

I'll up-date when I get to it. ( don't hold your breath! )

Thanks to Mary to pointing me to this thread. I just went to REI and grabbed the "Platypus Gravity Works" replacement filter. It's an uberlight little cartridge that, I believe, is intended to go inside the gray, bulky filter portion of the dual platy system. I also bought a platypus connector and hose.

My question is this, can I replace the in-line, seychelles filter on my ULA with this little guy and expect it to work as well as what is currently there? If so, I think I can deal with the "weight" of the silnylon and will have a perfect system so long as platy hoses mate with my ula bag/fittings.

Here's a pic:

I believe that filter only takes out the bad taste, you might check to see if it filters out the bad stuff like Giardia.

From REI's website:

"•Removes flavors, odors and many organic compounds from filtered water to improve the taste
•The Platypus GravityWorks Carbon element should be used to improve the taste of safe water sources only; element does not remove viruses, bacteria or protozoa from water"

This is a routine aspect of my day job (cleaning up toxic waste sites) and a carbon filter WILL remove gasoline, benzene, chlorine, and many pesticides.

It WILL NOT remove pathological organisms and the "plate counts" of bacteria will typical go UP after a carbon filter because of the tremendous surface area they give the biofilm to live on and because it dechlorinates the water passing through it.

It will improve the flavor and decolorize many waters. It may make it chemically safer. It will not protect you against biological issues. Pity, because it is small and compact!

It weighs so little I may just add it in line with the Seychelles for added/pre-filtration.

This is what I use now. Maybe David could chime in on this one.

Jack

David, you said "This is a routine aspect of my day job (cleaning up toxic waste sites) and a carbon filter WILL remove gasoline, benzene, chlorine, and many pesticides."

Does Carbon remove any metal/mineral contamination from mine runoff?

I have always heard that nothing will remove mine runoff contamination which is actually one of the primary issues in many Colorado and locations in the Western US in general.

The CR-100 claims effectiveness against micro-organisms although their website leaves me unclear whether it is the sintered carbon or some separate filter that blocks the passage of small particulars. The company is well known, the claims reasonable, and I would be fine relying on it for taste and biological treatment.

Combined with aqua Mira in more queationable areas, this may do the trick. A+ discovery wasabi for was that Platypus hosing fit the ULA reservoir.

The sawyer 3 in 1 filter is designed to go in the hydration bladder hose and normal suction on the bite valve will fill your mouth coickly. Unlike the platapous carbon filter it will filters out everything but viruses. All you have to do is stop fill your bladder, repack the bladder into your pack and go. The Sawyer 3 in 1 weighs 3 ounces.

Hi everyone, I'm looking for some knowledge and or help.
I used some leftover silnylon seconds to make a water bag for a gravity filter, and almost immediately after filling with water it begins to "weep" out of the fabric. I understand it is only water resistant and not water proof but I was wondering if this is common and just due to the weight of the water pushing out or did I get a bad run of silnylon?

Most silnylon isn't waterproof

"Shield" from thru-hiker.com is better

You could put silicone diluted with mineral spirits 10:1 and it would make it pretty waterproof, but then it would probably contaminate your water

I wonder if fabric in general is safe for water? Not designed for that. Any fabric might contaminate your water.

Maybe better to use water bag.

This is the direction I'll go, at least it will be an easy switch over. Thanks for the speedy reply.

Thanks Steven. I just ordered the Sawyer three way filter. It's time to replace the ULA/Seychelles filter - its heavy and has done its job long enough. I didn't like the squeeze system's looks. I know many do fine with it. This will definitely be a safer bet than the platypus carbon filter. Sawyer lists the weight @ 1.8 oz. well see about that. My ULA bag is silnylon and has never had a weeping problem. I still want to try and make a cuben replacement. But don't have the tools to add the trim and grommets needed for the drawstring. I think it would get pricey too. Will probably just keep the ULA until someone produces a cuben option or offers to build me one for cash or trade.

Edited by bcutlerj on 07/28/2012 15:28:39 MDT.

Randy:

Carbon as a slight affinity for metals, but not much. I've looked mostly at Arsenic (flavor of the local water and something I encounter in various spots in the Far- and Mountain-west USA) and carbon does reduce it a bit, but the % removal is small even in large-capacity carbon vessels (one-day residence time) that I use for work.

For metals, typically we use an ion-exchange resin. It is highly effective, and occurs quickly, but I'm not aware of a small-scale version. If one posed as an engineer doing a feasibility study and talked Westates or Calgon or some other vendor out of a pound or two, you'd be set for life but often they want you to send them many liters of the water and they conduct a bench-scale test to generate design specs.

Other options for metals are distillation and reverse osmosis. Either of which you might do for drinking water at home or cruising on a sailboat but never while backpacking.

I'd note though, that a microgram of infectious stuff breeds in your body and can make you quite sick from one exposure. While cancinogens and toxics are dose-related - more exposure is worse, less exposure is less risk. If you live in Fallon Nevade - TREAT YOUR WATER FOR ARSENIC!!!, but if you are just passing through, you'll have 1/365 x 1/70 the risk of a life-long resident.

UL for metals (and sorry, this is a campsite technique, not while hiking): a pinch of baking soda to raise the pH (acidified water dissolves MUCH more metal) and a pinch of alum (which can be bought cheaply in small quantity in very well-stocked bulk food / spice departments of health food stores). The alum allows all sorts of stuff to flouculate (clump together) and sink or rise in a water. The alum is edible - it is used in some cooking. It is amazing to compare side-by-side Colorado River water with and without alum for settling times - there's an easy 10-fold difference AND the alum-treated water is MUCH clearer of silt, metals, etc. Then skim the scum off the top and decant the clear liquid without disturbing the sediments on the bottom. Biological matter will also have tended to sink or rise, so the clear liquid will have a MUCH lower biological load, but while this would greatly reduce your bio exposure, it shouldn't be considered 99.99% effective like a good filter would be. (Your filter, will however, go MUCH longer between cleanings if you settle out the crud first).

Dave,

Could you tell us more about alum? There seem to be many alums. Which one do you recommend? How long does the process take (like 50% is 5 minutes, 80% in 20 minutes...) How much alum per liter? Alum seems like a good solution for me, since I use a siphon from a 3 liter water bag. Thank you.

TZ

This recent thread and my own curiosity prompted me to revive this older thread:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=67849

I'm curious to know whether anyone's tried using a ceramic element in a gravity flow system. I'm looking for something that's not necessarily UL, but low maintenance, will filter 5 months of water for 4 cyclists, and will take a beating.
I've considered MSR autoflow systems but the number of filters we'd go through deters me from that option. I'm also reticent to pick up a carbon filter for the same reasons.

Any thoughts?

Thanks,
Matthew

The life of any water filter is somewhat dependent on the initial clarity of the water and whether you use a prefilter (to catch the big stuff).

I've seen a new ceramic filter rendered almost useless within two quarts of water, simply because the water was grimy and there was no effective prefilter. If you know what you are doing, you will learn the quick filter cleaning method for yours.

--B.G.--