Welcome! Ultralight backpacking is my passion, and keeping up on new technologies, gear, and techniques relevant to UL backpacking is what floats my boat. I'm always looking for the lightest, most functional gear to improve a lightweight or ultralight backpacking kit, and report my impressions and field testing results here. For hikers wanting to keep up on the latest and greatest ultralight backpacking gear, this is a good place to hang out. Also, there is a lot of information here (and on our informational website Southwest Ultralight Backpacking) on useful techniques and backcountry etiquette -- food for thought for hikers wanting to lighten their load and their impacts.

My goal for Ultralight Insights is to understand, test, and report on new technologies and gear of interest to lightweight and ultralight backpackers. It's a passion after all, so we just plain enjoy talking about it. I hope readers will add their own wisdom and comments, respond to my questions, ask their own questions, and correct me if I get something wrong. Happy hiking! Will

Thursday, September 4, 2014

A Technique for Using a Steripen with a Hydration System

By Will Rietveld

My (current) favorite lightweight water purification system is the rechargeable Steripen Freedom, a 2.65 ounce (without carry case) device that purifies water with UV light. Why? – Because there is no wait time or sucking through a filter, just treat and drink.

I prefer to use a lightweight hydration system carried in a side pocket, but the flask has a narrow opening, which is not amenable to using a Steripen. The Steripen requires an open container or wide mouth bottle to wave the device around in the water.

So how do you use it with a hydration system, in ultralight style, which means minimal extra weight?

My ultralight backpacking friend Tom Galbraith came up with a clever and simple solution, described below. Here’s a photo of Tom on a recent backpacking trip two weeks after he bicycled 1700 miles on the Continental Divide road route. Credit for the idea goes to Tom, and I show the method here with his permission.

The technique is to use a gallon size zip-lock bag to scoop up water, treat the water in the bag with the Steripen, then transfer the water into your hydration reservoir. We like to use a Platypus flask.

Equipment needed is a Steripen, 1-gallon zip-lock plastic bag with slider closure, and a flask.

Scoop up water into the plastic bag. It’s easy to do while holding the bag open with two hands. I often treat 2 to 3 liters at a time and share the treated water with my hiking companions. For mountain hiking, I usually carry 1 liter or less to minimize weight.
Treat the water with the Steripen, which uses UV-C light to sterilize organisms. The Steripen Freedom uses a 48 second cycle to treat 1 pint of water, so multiple cycles are required, depending on the quantity of water. Simply dunk the Steripen into the water (it turns on automatically) and wave it around in the bag.

Transfer the treated water into the flask. If you are doing it alone, it helps to open the slider on the zip-lock about 1.5 inches, lay the zip-lock bag over your leg to support it, and pour into your flask held with the other hand.

This technique is a head-slapper in its simplicity and adds only a fraction of an ounce to your pack, besides the Steripen.

I have tried just about every water treatment and hydration system available, and this system is my current favorite. Its not the lightest -- Aqua-Mira drops or tablets are lighter -- but I like the convenience of fast treatment with the Steripen and being able to drink on the fly with the hydration system. In the mountains, where water is abundant, I treat and carry a liter of water at a time, which is a good balance of light weight and convenience.


  1. Excellent.
    Nice way to get rid of the wide mouth bottles - even the collapsible ones.

  2. I use vitamin water containers for water storage. I made an adapter for the steripen adventure by drilling 2 holes of the exact size in a vitamin water cap. This adapter slips on the steripen, I simply invert my full bottle of water with the adapter and pen on, and sterilize, then cover with an intact cap, or one that has a short length of platipus tubing and mouthpiece. No transferring of water.

    1. Hi Stephen. My friend Tom (mentioned in the article) also tried the cap adapter, and it worked well, so that's another option. And the Vitamin Water bottle is lightweight.

      I have found that the zip-lok bag method works well when I am sharing treated water with my hiking partners and also when I am getting camp water. That's because I can treat a larger volume of water conveniently. Of course it also works well for treating only 1 liter, but it does have the extra step as you mention.

      Thanks for your contribution.

  3. Thanks for shared it. It's a simple and intelligent idea.

  4. Hello Will. Wondered if you continue to have have success with your steripen as your primary purification method--a long-term review question. Many thanks.