One of our most frightening moments on the Continental Divide Trail was in New Mexico when we arrived at a water source called Adobe Springs to fill up, and the water was gone! The spring had gone dry. We were 12 miles (plus a hitch into a town) north of the last water source, and about 20 miles south of the next water. With less than 1.5 liters between us, we had to decide whether to walk backwards toward water we knew was there or forwards, crossing our fingers that an unmapped water source would turn up… We decided to go backwards on dirt roads that paralleled the trail hoping to find an earlier water source. After backtracking 11 miles, we found the muddy cow pond in the photo above. We would survive! Because of the 22 mile detour and the extra day on trail that it caused, we no longer had enough food. We had to add an additional town stop to our itinerary to resupply.
Sometimes you don’t know what a long-distance trail will throw at you, so being adequately prepared for the unexpected is always a good idea. This post describes our water filtration strategy ( Platypus QuickDraw or Sawyer Squeeze ), which so far has kept us hydrated (enough) and has prevented either of us from catching unpleasant waterborne diseases like Giardia.
Click to skip to section:
- Where to get water?
- How much water?
- Why do we filter?
- Our preferred method: hollow fiber filters
- Other water purification systems
Where to get water?
Properly water purification, like filtering, makes most water safe to drink. Clear mountain springs or streams taste the best and have the least filter-clogging sediment and algae, but lakes and rivers are fine sources for water collection too. We have collected water from beautiful sources, but also from cow troughs, green ponds, and even mud puddles in tire ruts when necessary. We always filter before drinking, and while hiking in the USA or Germany we haven’t gotten sick yet!
How much water?
As a general rule, we each aim to carry about one liter of water for every five miles of hiking. When it is very hot out, this isn’t enough, and when it is cool, this tends to be more than necessary — it is important to adjust according to conditions. Different hikers have different drinking/carrying preferences. Our preference is to study our maps and only carry as much as we need to get to the next reliable source. Water is heavy (1 L is 2.2 lbs)!
When we are camping away from water sources, which we do more often than not, we factor in an additional liter for dinner and another for breakfast (for two). Although camping away from water means carrying more weight for the final miles of the day to get to camp, it can be worth it for increased solitude and scenery.
Why do we filter?
Even beautiful looking natural water sources along the trail can be full of germs. Giardia was our main concern on the Pacific Crest Trail and Continental Divide Trail, but contaminated water can cause other diseases too. We knew several thruhikers who contracted giardia and had to take time off trail due to diarrhea and vomiting.
Our preferred method: hollow fiber filters
Hollow fiber filters like the Platypus QuickDraw and Sawyer Squeeze are our go-to type of filter for thruhiking. They are lightweight and durable, and they can be maintained in the field. They do come with a few drawbacks, which are highlighted below.
What is a hollow fiber filter and how does it work?
Hollow fiber filters are made of tubes with tiny pores that water can squeeze through but bacteria and protozoa can’t. They usually have a clean side and a dirty side. On the dirty side, unfiltered water is forced (or sucked) into the hollow fibers, and on the clean side filtered water exits. Unsafe biological contaminants including bacteria such as e. coli and salmonella, and protozoa such as Giardia, are caught by the hollow fibers and never make it through to the clean side. Most hollow fiber filters have tubes that are too large to remove viruses or chemical pollutants, so these filters are not a good choice in areas where those are a risk. On most long-distance trails in the USA, such as the Pacific Crest Trail, Appalachian Trail, and Continental Divide Trail, pollutants and viruses are not a major problem, so hollow fiber filters are great for these treks.
Filter maintenance
Hollow fiber filters require some maintenance. As the filter removes particles and contaminants from the water, these accumulate in the fibers and need to be removed. For most hollow fiber filters, this is done by “back-flushing”, which is the process of forcing clean water backwards through the clean side of the filter. It essentially amounts to running the filter in reverse. Back-flushing is simple and quick, and usually improves the flow-rate of a filter.
For filters that are very clogged, it can help to gently tap the filter on a hard surface between back-flushes to loosen stuck particles. Tapping a filter too hard can break the filter or the fibers inside (Renee learned this the hard way when she punctured her Sawyer Squeeze on the CDT)!
Some manufacturers claim that any filter can be restored to it’s original flow-rate through backflushing, but in our experience this is not the case. We have gone through several Sawyer-brand filters that were extremely clogged and no amount of back-flushing improved the situation.
Hollow fiber filters will break if frozen. This makes them a poor choice for winter hiking. When freezing temperatures are a threat but not the norm, for example early or late in the hiking season, we avoid letting our filters freeze by sleeping with them in our sleeping bags overnight. If it is still below freezing during the daytime, we hike with the filters in a jacket pocket. (We also learned this the hard way by leaving our Sawyer Squeeze outside on a below-freezing night.)
Filter brands/models
Recently we discovered Platypus QuickDraw filters, which are new in 2021. After testing them for over 1000 miles, we like these a lot! They have a higher flow-rate than any other hollow fiber filter we have used, and in contrast to most hollow fiber filters, there is a way to check if they have been broken through freezing or dropping. They are also easy to back-flush. They include caps on both ends which is convenient for keeping the clean side from getting contaminated and keeping the dirty side from leaking into a sleeping bag on cold nights.
Sawyer filters, including the Squeeze , Mini , and Micro , are very popular on long-distance trails. They are simple and light. In our experience the Squeeze is the only Sawyer with an acceptable flow-rate, but even this filter clogs relatively quickly and can be hard to restore to a good flow-rate. Sawyers have been around for a long time and are very popular among long-distance hikers! (We have tested the Sawyer Squeeze for ∼5,000 miles and the Sawyer Mini for ∼2,650 miles.)
Other brands of hollow fiber filters that are frequently seen on long-distance trails include the Katadyn BeFree line of filters and LifeStraw filters, but our experience with these is limited.
Other water purification systems
Here are a few other water purification methods we’ve used, but there are many others out there…
Water Purification Tablets
Water purification tablets are lighter and require less work than water filters. They use chemicals like Iodine or Chlorine Dioxide to kill bacteria, protozoa, and viruses. You just put a tablet in your water bottle and wait about 30 minutes (see manufacturer’s directions). The downsides are you have to wait, they do not get rid of sediment, and some may make your water taste funny.
Ceramic Filters
Ceramic pump-style filters are also available on the market. You do not have to worry about freezing these filters. The downsides are that these are bigger and heavier than most of the other options mentioned in this post.
Boiling
Boiling water also kills bacteria, protozoa, and viruses. If you are already bringing a pot, stove, and fuel for cooking, no extra gear is required. The downsides are you have to wait, use fuel, and boiling does not rid of sediment.
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