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Other uses for gravity filter water bag?
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Colin Krusor
(ckrusor) - M

Locale: Northwest US
Other uses for gravity filter water bag? on 05/09/2012 23:52:28 MDT Print View

I'm putting together a little MYOG gravity filter with a water bag that will be either silnylon or cuben. Before I decide on a material and a design, I'd like to find a way to make the bag serve more than just this purpose. I have considered the obvious options (stuffsack, pillow, sleeping pad inflation bag, etc.). Has anyone made a water bag and successfully used it for these or other purposes?

Ray Bailly
(tempestv) - F
bucket on 05/10/2012 06:31:28 MDT Print View

I'm in the process of putting together a gravity feed water system that will use a collapsible bucket as a reservoir. It will also be useful for all the things you might use a bucket for besides carrying drinking water, such as water for putting out the fire, wash basin, bear bag (fill with cold water to keep perishables cold), ect.

Mary D
(hikinggranny) - MLife
Other uses for gravity filter water bag on 05/10/2012 11:11:06 MDT Print View


jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Other uses for gravity filter water bag? on 05/10/2012 11:26:05 MDT Print View

Maybe rather than gravity filter, the Sawyer Squeeze is better.

Put untreated water in one bag. Squeeze water out of bag, through filter, into small water bottle.

You don't need a second bag. Weight of Sawyer Squeeze system may be a little less than gravity system.

Another thing is, with gravity system, you turn untreated bag upside down and all the sediment settles into the filter, clogging it up. If you left Sawyer bag right side up, let sediment settle, and then carefully tipped bag over a little, you could leave sediment at bottom without clogging filter.

Mary D
(hikinggranny) - MLife
gravity filter water bag on 05/10/2012 11:35:01 MDT Print View

You don't need a "clean" water bag with a gravity filter anyway. Just filter directly into your water bottles. I never could figure out why commercial gravity filter systems all have that unnecessary and heavy "clean" bag!

I plan to take a look at the Sawyer squeeze filter for solo use (the gravity filter is much better for groups), but I need to find out just how much squeezing is needed. I don't have a lot of strength in my hands, so if it takes a lot of hard squeezing to get the water through, forget it.

Ray Bailly
(tempestv) - F
sediment on 05/10/2012 11:39:26 MDT Print View

The squeeze system would be handy at times, but not as nice as a gravity system for large amounts of water. As for sediment, the solution with a gravity feed system is to hang the reservoir, let the sediment settle out, and then drain a little water out without the filter attached. This way, most of the sediment is drained off on the ground, not through the filter. On my Gravity feed system, I'm going to set the drain a little ways up the side of the bucket, which will allow for room below the drain for sediment to settle into.

My plan is to fill the bucket the night before with cold water, put any mildly perishable food in the cold water, and hang the whole thing as a bear bag. In the morning, take the food out, and filter the sediment free water.

My filter setup is designed to unhook from the reservoir using Camelback QD fittings. I can then take a 1L Platypus bladder with the same fittings and have a squeeze system.

Edited by tempestv on 05/10/2012 11:44:47 MDT.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Gravity filter water bag on 05/10/2012 14:16:29 MDT Print View

Jerry, I just plan to use one bag (for dirty water), and filter directly into my water bottles.

I think my gravity filter setup, everything included (water bag, tubing, valve/clamp, fittings, filter, etc.) might turn out to be in the same weight neighborhood as the Sawyer squeeze.

The filter is a Barnstead inline polyethersulfone hollow fiber filter, exactly like the Sawyer but smaller. Despite the smaller size, with 5 feet of tubing above it, the filtration rate is plenty fast. I've tried it twice and it took 77 and 71 seconds to fill up my 1 liter bottle. Like the Sawyer, it will filter millions of liters of water, and only require occasional backflushing to keep it clean. The tubing is thin-walled polypropylene rather than the heavy vinyl tubing that many gravity setups use. The tubing is tough but collapsible, so the filter has to go at the bottom. I attached a threaded cap to the filter so it screws directly onto my platypus bottle.

I just ran some water through it and then weighed it. With everything (filter, fittings, clamp, and five feet of tubing) except the water bag, and wet, it weighs 1.4 oz. It is right around one ounce when dry, I think. But it will be carried wet, so I think, for water filters, wet weight is more relevant than dry weight.





With a 2L silnylon or cuben water bag, the whole thing should come in under four ounces, I think. The fittings are arranged so the tubing can be removed and the bag can be attached directly to the filter, to function like the Sawyer Squeeze if I don't want to wait for gravity.

So, I think it would be clever to use the water bag for other things as well, and I'm interested in any experiences that anyone has had using their gravity filter water bag for other things, and what, if anything, they had to do to it to make it functional for other uses.

Edited by ckrusor on 05/10/2012 14:21:05 MDT.

Mary D
(hikinggranny) - MLife
Other uses for gravity filter water bag? on 05/10/2012 15:49:50 MDT Print View

You probably don't want to use the wet "dirty" water bag as a stuff sack! It will undoubtedly be wet when you pack up in the mornings, especially if there's water in it overnight. Remember also that it has "dirty" water in it, so you don't want it in contact with anything that might end up in or near your mouth. If you're going to hang food inside, make sure it's tightly sealed and remember that the outside surface of whatever you seal the food in--plastic bag?--is potentially contaminated. That's why I consider mine as a single use item (except as a possible shower).

I'm really interested in your filter; how many microns is it? Source?

Edited by hikinggranny on 05/10/2012 15:53:33 MDT.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Water bag and filter on 05/10/2012 17:19:10 MDT Print View

Mary, I agree with you about the hazards and complications of using the dirty water bag for other things. This, I think, is the major obstacle to having a multi-use dirty water bag. I wondered if it could be turned inside out, so (most) of the dirty water on the material would be on the outside. As you said, it would be wise to keep it away from things that will be in contact with your mouth. I think it would be no more risky than one's shoes, though, or the bottom of one's pack. Maybe, turned inside out, it could be used as a sleeping pad inflation bag (no topping off by mouth afterward) or a tent stuffsack?

The filter is a 0.2 micron filter. It has larger pores than the Sawyer Squeeze filter (which is 0.1 micron), but there is no functional difference. Neither will filter out most viruses, and both will filter out all cellular waterborne pathogens. In microbiological labs, filters with 0.2 micron pores are considered “sterilizing” filters. No pathogenic waterborne bacteria (even spore formers and the narrowest bacilli) will pass through (this is actually a complex issue involving motility, Brownian motion, etc.). When backpacking, I am concerned about protozoans, helminths, and bacteria. In remote areas, I don’t consider waterborne viruses a major risk. Almost none of the water filters available to backpackers will remove viruses. One of the benefits of the 0.2 micron pore size (as opposed to Sawyer’s 0.1 micron pores) is greater flow rate. This is the reason that my little filter is as fast or faster than the much bigger and heavier Sawyer Squeeze filter.

This filter is made by Barnstead, and I don’t know the product number. We use them in the lab for filtering tissue culture supernatant. I don’t know of a good consumer source, but non-reagent lab supplies like this are often available online in small quantities. A google search would probably turn some up. I don’t know what the price would be per filter. Sorry for not having a good source for you.