Top 3 ways to purify water on a DofE expedition
There are a lot of options when it comes to expedition water treatment, from gravity filters to purification tablets to UV light. In this article I’ll go through the top 3 ways of treating water on your expedition and why they’re the best, as well as discussing the options that didn’t make the cut, so no stone is left unturned.
For expeditions less than a week long, purification tablets are the simplest way of treating water, but involve a wait time before the water is fully drinkable. Human-powered filters are the best alternative if you want the water to be drinkable immediately.
What’s the difference between purifying and filtering?
Before we get into what makes certain methods better than others, its important to understand the difference between the two ways of treating water: purification and filtration.
Purifying water doesn’t remove harmful impurities (bacteria, protozoa and viruses) — it kills them, making the water safe to drink. If there is any sediment or dirt in your water, purification won’t remove it. This means that from some sources you will have to prefilter the water through a bandana or piece of cloth to remove the sediment. In the UK, it is unlikely you will be taking water from sources where this will be necessary.
Filtration does the exact opposite. It makes water safe to drink by physically removing the harmful impurities and sediment as it passes through a semi-porous filter. While bacteria and protozoa are removed during filtration, viruses are not as they are too small. This is generally not a major issue unless you’re intending to drink some (really) nasty water.
The best 3 methods
1. Water purification tablets
Pros: easiest process (by far), cheap, super lightweight and compact, kills viruses
Cons: wait time, may affect flavour, doesn’t filter sediment
Spoiler alert: water purification tablets (specifically chlorine dioxide tablets) are the way to go for sub-one-week expeditions. The reason expedition length makes a difference is because a multiple month long hike would require carrying a lot of tablets — and at that point it may become preferable to simply look for a reusable system, like a filter.
The best aspect of water purification tablets is how easy they are to use. You pop the tablet in the water, give the bottle a shake, wait a bit, and that’s it. They also weigh next to nothing and are the cheapest option for an individual expedition.
Some people may be concerned about the flavour. If you’ve ever been through the quite jarring experience of drinking some water that unexpectedly tasted exactly like a really chlorinated swimming pool, I understand your concern. The good news is that, after 10 days of use over two Gold DofE expeditions, not once did I notice a funny flavour in my water. I was really — like really — impressed.
I used these chlorines dioxide tablets by Lifesystems and have no criticisms at all: they are fairly priced and do the job perfectly.
The one real drawback with water purification tablets is the wait time. For the Lifesystems tablets I used you add one tablet per litre of water, and the wait time gets exponentially longer the more tablets you need to add. For one tablet (i.e. 1 litre), the wait time is 10 minutes, but for two tablets (i.e. 2 litres) it’s 30 minutes. You could, in theory, treat two litres of water in 10 minutes by purifying two separate one-litre containers simultaneously, although I wouldn’t bring extra bottles on your expedition for this sole purpose.
Chlorine dioxide tablets by Lifesystems come with this handy case. It also has instructions on the inside, in case you forget how long you need to wait.
2. Human-powered filter
Pros: no wait time, lightweight, won’t affect flavour, filters sediment
Cons: process can get annoying/tiring, slow to filter large amounts of water, doesn’t kill viruses
You may decide that it is important for you to have water which you can drink from the source instantly. For this purpose I would recommend a human-powered filter. Although they are certainly more expensive than purification tablets, a filter will (almost) never run out.
There are a range of options within the human-powered filter category, but one of the best are Sawyer filters, because of their flexibility and reliability. A Sawyer mini can screw directly onto the cap of a standard plastic bottle, allowing you to drink the untreated water directly from the bottle as it passes through the filter. If you don’t have a bottle, the Sawyer comes with it’s own screw-on pouch too.
For those who prefer to drink from bladders rather than bottles (such as myself — find out why in my post about water on DofE) you can use the Sawyer Squeeze with the associated hydration pack adaptor to create an inline filter in your bladder’s hydration tube, allowing you to drink untreated water directly from the bladder — that’s pretty neat. This video by Sawyer explains how you can add a filter to your bladder’s hydration tube.
3. Boiling (sometimes)
Pros: simplest method when already intending to boil water, won’t affect flavour, kills viruses, free
Cons: extremely inconvenient if not already intending to boil water, doesn’t filter sediment
Firstly, boiling water is not going to be your primary method of treating water. So why has it made my top 3, you may ask? Because there will be situations when you are already going to be boiling water for non-purification purposes.
On an expedition it’s important to be as efficient as you can, and this means not treating water when you don’t need to. If you are boiling water to make a mug of tea in the evening or to prepare your boil-in-a-bag dinner, you can use water directly from the source (if it’s nearby), because the heat will kill any bacteria/protozoa/viruses.
As a quick disclaimer: warming up your water doesn’t count as boiling. Water must come to a rolling boil for one minute (and longer at high altitudes) to be considered safe to drink.
What didn’t make the cut and why?
LifeStraw
LifeStraw have diversified and now do a number of filters similar to the ones made by Sawyer — there’s no issue using these. What you shouldn’t be buying is the original LifeStraw, which is a filter where one end goes in the water source and you drink through the other end. It is not designed to be attached to a water bottle.
The issue with this is that you cannot get treated water into a bladder or bottle (at least not hygienically — I’ll let you work it out). As you can only drink water directly from the source, this is clearly not a viable option.
Gravity filters
I know someone who used a gravity filter on their Gold DofE expedition, and he says it worked well. After seeing the filter being used though, I concluded that he only brought it with because he already owned it. Gravity filters work by filling a pouch with untreated water and hanging it from a tree (or similar object), then letting the water naturally drip through the filter into a second pouch at the bottom.
Although you can filter multiple litres at once, which is a bonus, you still have to wait a long time — often longer than with the purification tablets. And on top of that, unlike with purification tablets where you can continue to hike whilst the tablets ‘do their thing’, a gravity filter paralyses you to one spot until it’s finished. Oh, and what if there aren’t any trees around?
UV light purifier
UV light purifiers essentially do the same thing as purification tablets: they kill all bacteria/protozoa/viruses in your water. The reason this method didn’t make the cut is because it’s hard to justify ever using it over chlorine dioxide tablets for an expedition no longer than a week.
UV light purifiers are heavy (relative to purification tablets) and require batteries to operate, which means you also need to bring spare batteries. Until you are embarking on an expedition sufficiently long that the number of purification tablets you require is equal in size and weight to bringing a UV light purifier plus the necessary spare batteries, I’d give this one a miss.
The verdict — which is best?
At this point you may be able to guess what the verdict is. These chlorine dioxide tablets are the way to go for expeditions under one week long — i.e. all DofE expeditions. If the wait time associated with purification tablets is a major issue for you an issue, the next best option are is the Sawyer Squeeze or Sawyer mini.