Gravity Filters and SteriPens?

10:26 p.m. on July 26, 2010 (EDT)
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I've recently been looking for a good water filter for myself.. but I still have a few questions about the actual purifying/filtering process. First off, will a gravity filter clean the water enough for drinking? I've seen some discussions between "purifying" and "filtering", and tey've confused me quite a bit. Also, would I need to filter out water before using the SteriPen on it? Thanks in advance!

11:28 p.m. on July 26, 2010 (EDT)
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You should read my series of articles here on Trailspace, particularly the fourth one which covers treatment methods. The terminology can be confusing, especially since some of the treatment method manufacturers are pretty loose with the terms.

"Purify" correctly used means to purify to surgical standards.

"Potable" means to treat to the point that the chance of suffering ill effects (whether from critters or from chemical contamination) is minimal.

"Sterilize" means that all the critters are dead and/or completely removed (it says nothing about chemical contamination, just the biologics).

Strictly speaking, you cannot completely purify water in the field. The reason for this is that certain bacteria encapsulate themselves under certain conditions and cannot be killed by boiling, UV, or chemical means. A fine enough filter (not practical for backpacking) will remove them. Luckily, these bacteria do not cause ill effects on humans.

Also, certain protozoa have a cyst phase that protects them against chemical treatment, though boiling and UV inactivate them to the point that they usually will pass on through your system without harm.

More directly to answer your questions - Yes, a gravity filter (one of the higher quality ones with fine enough pore size) will make the water potable. So will the pump filters (again, fine enough pore size). The filters that "purify" the water use an iodine resin matrix to inactivate the remaining viruses (which are small enough to get through almost all backpacking filters - pump or gravity). This makes them problematic for long-term use for people sensitive to iodine.

The SteriPen requires the water to be fairly clear. But letting the water settle overnight and decanting while filtering through a couple layers of coffee filter paper will take care of this, according to the SteriPen people - you do not need a pump filter or gravity filter in addition.

Most important source of intestinal problems in the backcountry, though, is not the drinking water. It is personal hygiene - wash your hands thoroughly before handling food, especially if you are the designated cook for the meal. If you are not going to use soap and water, at least carry a container of a hand cleaner, such as Purell or one of the other alcohol-based cleaners. In Antarctica, where we had to melt snow and ice for all our water, the water was too precious to do soap and water washing (and it would freeze anyway). So everyone had their personal bottle of hand sterilizer and the latrines in the fixed camps had large pump bottles of it. We had no problems during our 6 weeks on the ice. Filters don't work in such conditions, so we largely depended on the pasteurizing approach - water raised to 155F or hotter will be pasteurized to the point of being potable.

1:12 p.m. on July 28, 2010 (EDT)
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693 forum posts

Bill's excellent response covered everything you need and more. However, if you are really OC, set up a solar still for your camp. You can make one easily and the components are lightweight. The distilled water is free of all but H and O (and all the microbes in the air inside the still that collected when you opened it).

Or you could do what we did as kids - never drink any running water that hadn't flowed over seven pebbles. Hey, it seemed to work...

3:41 p.m. on July 28, 2010 (EDT)
389 reviewer rep
1,124 forum posts

Im using a system of pump or gravity flow, and tablets. With the research that I have done I think that this should make most water very save for drinking. Im using a very cheap filter to get out everything bigger that 2 microns. And the tablets to kill the rest. The cost need not be overwelming. I've spent just over $30. Altough the NFS in my area says most the water is ok, they do recommend the use of a filter. So I do overkill a bit. Most the water I use is boiled for cooking also. It is wise to talk to people in the area that you are going, to see what you need in that area.

12:57 a.m. on July 29, 2010 (EDT)
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35 forum posts

If you notice in the advertising photo, there are NO DROPLETS on the glass, above the water line… Because they will NOT be cleaned.

Cautions not listed or explained in the instruction booklet.
When you dip your Nalgene bottle into the source water, the threads get contaminated and therefore the cap gets contaminated too, when you put the cap back on. Any spillage over the top, or water droplets above the water line in the container are suspect contamination. Micropur (and other products too) recommend after dissolving their product in the water, that you crack open the bottle while holding it upside-down and let a bit of water flow out of the cap. The activated cleaning solution then cleans the cap and threads on the outside where you put your lips. All the water inside the container is cleaned too, not just the water below the water line.
Instruction page #4, Item #5 says:
• “SteriPEN is not intended to disinfect water above the surface of the water in the container, i.e., droplets of water suspended on the side of the container.” Caution: You can not clean the cap and threads or water droplets above the waterline with the SteriPEN product. Note: The product is designed to kill all micro-organisms. Giardia lamblia is 2 microns. They could be anywhere where there is even the smallest speck of water. Instruction #4 on Page 1, says:
“Note: If visible light is not evident, SteriPEN’s lamp is not on, and water should not be consumed.”
Caution: The light is extremely difficult to see when you are in bright sun, even if you shadow the product with your body.

1:00 a.m. on July 29, 2010 (EDT)
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35 forum posts

My SteriPEN went back to the store.

2:04 p.m. on July 29, 2010 (EDT)
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14 forum posts

I have many hours on my SteriPen and I am totally happy with the finished product. Like so many other subjects concerning our time out of doors it seems to me tha each of us have to decide to what means we will be willing to go to to produce an end result that we can live with. I have met numerous hikers who just laugh at the whole water thing and drink directly out of what ever sourch we are currently at and have been doing so for years. Personally I'll pass on that one, but I understand their point. So, good luck Joe--do your resurch and go with what feels best to you.

8:14 p.m. on August 4, 2010 (EDT)
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28 forum posts

Very satisfied Steripen user here.

Most of the places i backpack filtration is unnecessary making my Opti optimal.

May 23, 2018
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