MSR AutoFlow 4L Water Filter

Pros Fast Effortless 200-denier Cordura dirty water bag (durable) Large fill opening, easy fill Adjustable hanging strap Pre-filter Light weight (14 oz) Armored filter Bottle adapter included

Cons Clean water bag not included Difficult  roll type closing (think dry bag) No charcoal option 4L of water at camp Difficult to back flush without added clean bag

Used this filter for the first time in the High Uinta Wilderness area near Young Lake at 10500 feet.

The filter is composed of one bag made of a red 200-denier Cordura® with a clear window marked with liter fill lines.  The opening goes from edge to edge of the bag making the dirty water bag easy to fill.  In fact I had problems (good problem to have) with overfilling it and needing to dump water in order to close the opening.  That brings me to the roll closure.  Just like any dry bag, this water bag closes with a 4-roll method.  The main problem with rolling is not that it leaks (it does not), but it traps air making the closing very difficult.  I learned to squeeze the air out by placing the bag on a surface and collapsing the bag until water was near the opening, then begin rolling of the bag.  Once you master the closing, the closed roll becomes a help in carrying the bag.

The hang strap attaches to one side of the buckle used to close the roll, which essentially becomes the center of the bag after rolling and connecting the closure buckle.  The hanging strap is adjustable with a quick release.  Very nice.

The dirty water bag also includes an integrated pre-filter to keep large particulate from the hollow fiber filter, a very nice feature. This pre-filter is a micro screen that is easily cleaned.  The filter connects with a quick release, self closing connection.  Disconnecting the filter does not leak water out of the bag.

One major drawback is the filter does not come with a clean water bag.  You must add one as an add-on if you desire to store filtered water.  I added the a 4L dromedary to increase camp water to 8L.  I'll review the dromedary bag in another article.  For now let me say I was disappointed with the overall utility of the bag (as sold).  The dromedary bag also needs at least one optional accessory to make it worth owning.

Filtering 4L liters took only a few minutes.  Since I was using the dromedary bag I needed to attach the (included) bottle adapter.  The dromedary bag was a wide mouth opening similar to a Nalgene bottle.

Back flushing to clean the filter (recommended ever 8L) was simple since I had the dromedary bag.  Would have been very difficult, if not impossible otherwise.  You need filtered water to flow back through the filter to back flush, and without a "clean water container" this would have been nearly impossible.

Platypus charcoal filter could be added if desired since MSR does not produce a charcoal accessory.