A water filter is a key piece of gear on nearly any backpacking trip. Many of these filters using a pump which moves the water through the filter and into your bottle. This design has its drawbacks as it may take a good amount of time and effort to pump all the water that you need for cooking, cleaning, and drinking. There is also the potential for part of the pump mechanism to break, something which could force you to have to boil all your water, take the "Giardia Challenge", or just be thirsty for the rest of the trip.
In this Instructable I'll show you how to use your existing water filter as a gravity powered water filter. This setup will use gravity instead of you to "pump" the water, be lighter, and be less prone to failure as there are no moving parts!
Step 1: Assemble Parts
First of all you want to get your water filter out and take it apart. In my case, I'm using a Katadyn Hiker Pro water filter, but this Instructable could work for other filters as well. The parts that we're looking for is the actual filter (the core which is screwed into the pump body) and the clean hose which connects the filter to your bottle. Unscrew the filter core from the body and connect it to the hose to complete your gravity filter assembly. Couldn't be simpler!
Step 2: How to Use Your Gravity Filter
Now what do we do with this thing? It takes a little more thought to make this work that your average filter, but is pretty straightforward nonetheless. The main idea is to place the filter in a pot of water above the bottle (or whatever water container you are using) and allow gravity to move the water. The idea behind this is the siphon principe: http://en.wikipedia.org/wiki/Siphon. The steps to get his all to work are as follows;
1. Put filter in a pot of water above the bottle.
2. To start the flow of water, there must not be air in the hose, so suck water into the hose with your mouth
3. Place end of hose into water container.
Once the flow has started it will continue until the pot is empty. To filter more than one pots worth of water, simply add more water before the pot is empty and air enters the hose.
Tips for use:
Remember that your pot has touched unfiltered water, so be sure to heat something all the way to a boil before you eat from it!
This technique takes a bit longer than pumping, so its often most convenient to do in camp while doing other things like preping dinner.
To make the water move through the filter faster, increase the vertical distance between the filter and the bottle.
Even if you don't use this technique regularly, remember it in case your pump breaks- it has happened to me before!