Mechanical water treatment

Continuing the focus on water, a really good quality mechanical water treatment pump makes filtering easy, and they are not very expensive. The three types of mechanical devices to treat water, their effectiveness and Micron rating are:

  1. Filter – Removes Giardia, large protozoa and some bacteria. (1.0 – 4.0 micron)
  2. Microfilter – Removes microorganisms, including protozoa & bacteria. (.3 – 1.0 micron)
  3. Purifier – Removes microorganisms, including viruses. (< .018 micron)

Read the box carefully. The nomenclature can be confusing. The street name for these devices is “water filter.” However, as you can see above, the technical name implies distinct capabilities. Filters can remove bacteria and protozoan cysts. Purifiers can do this and remove viruses. In most American and western Europe water sources, viruses are not present. The US EPA requires that a device labeled as a “purifier” remove viruses (with a rigorous EPA documentation proceedure). Be sure to read the literature to make sure if Giardia, Cryptosporidium and other microscopic pathogens (disease-causing agents) will be removed. Giardia will be your biggest concern at Yosemite. A 0.3-micron pore size or less is regarded as the optimum. The sales staff at your outfitter can help you sort this out. There are many brands to choose from. A good unit will be lightweight and compact. Many come with a pleated cartridge filter and a bottle adaptor. You should be able to pump one quart per minute. The life of its cartridge depends on the quality of water you’re trying to filter. The cleaner the source, the longer the filter will last. Still water is better than moving water because the “harmful elements” tend to sink rather than circulate as they do in moving water.

You will have a choice of several models from various manufacturers. Some models have a piston type pump mechanism, others use a lever. Some have outlets that clip directly into the standard size wide-mouth water bottle. Some have a small container of granulated charcoal near the outlet that improves taste. Higher priced models are light and pack small.

To clean your filter pump, I suggest cutting a large hole in the top of a half-gallon plastic milk bottle. Fill it with tap water and add a capful off household bleach. Then put your inlet and outlet into the water and circulate-pump it for about 5-minutes. This will flush the system with bleach to kill any hitchhiking bacteria. I also bring a small zip-lock bag to store the “clean” end of the system, so it doesn’t get it contaminated by the wet, “dirty” stream water while carrying the filter. If your filter is clogged, it will take longer to pump (a sign that cleaning is needed). Follow the manufacturer’s instructions on how to place the intake in the stream. You’ll be amazed at the great job that these do with a small water source. Water filters will be effective for about 200 gallons provided you don’t pump water loaded with sediment.

Ultraviolet light

A relatively new technology for portable water treatment is the use of Ultraviolet (UV) light. UV technology has been used for decades by many cities in their municipal water treatment plants.  When exposed to the proper wavelength, the DNA of the microbes is affected such that they cannot reproduce. Without reproduction capabilities, the microbes can’t make you ill.

A company called Hydro-Photon introduced the portable UV water purifier, with the brand name SteriPEN®. They market several models that can destroy over 99.9% of bacteria, viruses and protozoa such as giardia. These UV purifiers are effective and battery powered. The “Little Spring” water source is too shallow to scoop water into your bottle, so you’ll need to use a ladle or other method. The water treated by UV needs to be as clear as possible to prevent pathogens from “hiding” behind sediment. It’s best to agitate the water during the treatment.  The optimum method for unclear water is to employ a two-step process by first filtering suspect water, thereby removing the particulates, prior to using UV purification.


Unrelated thought worth quoting: “Ch-ch-ch-ch-changes Turn and face the strange. Ch-ch-changes Just gonna have to be a different man Time may change me, but I can’t trace time.” – David Bowie

*MrHalfDome™ – Rick Deutsch –

One Best Hike: Yosemite’s Half Dome


About Mr Half Dome - Rick Deutsch

Mr Half Dome. Has written the only half dome hiking guide, One Best Hike: Yosemite's Half Dome. Has hiked it 31 times to day. Lives in San Jose, CA Available for presentations. Carpe Diem Experience, LLC
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4 Responses to Mechanical water treatment

  1. The Steripden seems like the perfect little camping/hiking tool. Just be sure to bring spare batteries – it would be bad news were the batteries to run out!

  2. Maureen L says:

    thanks for the thorough review and update on this topic.

    a few things that may be specific to my MSR Sweetwater microfilter:

    it had to be prepped before first use in the field. easy to do; brush the cartridge with the cleaning brush and then pump water to get any carbon bits out.

    as the instructions suggest, I keep the ceramic filter cartridge in the freezer between trips, and then pump a bit to be sure it’s good to go for the trail.

    MSR does make a purifier solution if viruses are a concern (which they can be on international trips). however, dilute bleach works just as well.

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