There are of course a number of means of treating water and each has their benefits and drawbacks.
- Boiling water - requires a collection and storage vessel and a stove (or fire) and a pot in which to boil the water
- Treatment tablets or drops - Treats a limited amount of water, has a limited shelf life, often leaves a foul taste in the water
- UV treatment pens - Will destroy bacteria, protozoa and viruses. Light weight and compact. Will not remove chemicals and toxins. Expensive and dependent on battery power
If your travels take you to places where waterborne viruses are an issue (Asia, South or Central America, Africa), then the UV Treatment Pens are probably a good investment with some form of treatment for chemical/toxin contaminants, just pack extra batteries. However, waterborne viruses aren't such a big issue in North America (unless you are camping along a waterway with an upstream sewage outflow). For most of us heading to the mountains or distant lakes this isn't a concern which makes filtration units a better and more economical solution.
Last year I purchased just such a device, the MSR (Mountain Safety Research) Miniworks EX. I'll say right from the beginning that the first one I bought failed on my very first trip resulting in me having to cut my outing short by two days. The pump pivot pin broke and though quite a drag, the good folks at REI replaced it, no questions asked, with a brand new filter unit. They said they'd had two others returned for similar failures. Likely a bad manufacturing run on the pins, things like that happen in production. They made it right. I'm happy. Since then I've used the filter on a number of trips and I feel that I can now offer an honest review of the product.
What You Get
The unit comes as shown above with a pump body, 4 feet of hose, a weighted hose end with pre-filter, a float, outflow cover and filter gauge (the red crescent in the first image), filter (inside the pump body), a cleaning pad and a drawstring sack to keep everything contained in your pack.
How It Works
The pump draws water through the pre-filter on the hose end to remove any large debris/sediment, the water passes through a ceramic/carbon filter element, then through the displacement pump and into any common container with a mouth the size of a Nalgene bottle or one of MSR's "Dromedary" water containers.
Debris and sediment is trapped on the surface of the ceramic/carbon filter element (shown below). The filter is cleaned by using the cleaning pad (scotch-brite) to abrade the surface of the ceramic, cleaning away debris, sediment and with each cleaning a fraction of the filter surface area itself. Hence, the filter is a consumable item (replaceable via ordering from MSR or at any MSR retailer). The outflow cover contains a gauge (the red crescent in the first image) that allows you to determine when the filter is at it's replacement size.
MSR claims that the filter will remove particulates/sediment, chemicals/toxins, protozoa and bacteria. Viruses are not removed hence if you feel your water source might contain viruses you should use a UV pen or boil your water as well. MSR claims that the pump/filter will process 1 liter per minute and that the filter has a maximum life of 2000 liters with regular cleaning.
The aforementioned failure aside, Ive been pretty happy with it. The unit is light enough for me (canoe packs not backpacks) at 1 lb and only takes up 3x8 inches in the pack. It's American Made which is something of a rarity with all products these days, not just outdoor products and I rather like the fact that my money is going to someone in Seattle instead of Sri Lanka or Shanghai. The claimed water processing rate is overstated, but not by much. It takes me 1.3-1.5 minutes to pump 1 liter of water at a fairly vigorous pace. Not a big deal if you are just filtering water for yourself, and if your source is fairly clear, but if you are doing so for 2-4 people or your water sources are more cloudy you really ought to look into a filter with a higher flow rate and more filter surface area. Just know, it likely won't be as compact and light as this unit. The flow rate does slow considerably as the filter media picks up debris. That's good, it means it's not getting into your water container, but it does reduce the pace at which you can pump water. But because it is field maintainable, a quick cleaning returns it to peak flow.
The Miniworks EX does have limitations. If your use case fits within those limitations I strongly recommend the product for a solo adventure or emergency kit. However, if you need to purify water for a number of people you should seek a larger, more capable unit.