ON CHANGING THE FILTER MATERIALS – Please see the full answer below.
This filter MUST be used with some chemical means or boiling to make the water safe. This filter is only the first step, a pre-filter, before chemical
I get this question often, “How many liters/gallons before you have to change the filter elements?” The answer is not so simple, it all depends on what you pour into the top of the filter. If you are putting fairly decent, clear running stream water into the filter the activated carbon will last a long time. If you are filtering stagnant pond water not as long.
The synthetic fiber wad in the top will get dirty looking after a few days and if there is a high quantity of algae in the water will slow the filter down. I carry extra fiber to replace that in the field. You can also remove the fiber wad and wash it out in clear water if it has large debris in it.
I don’t normally carry extra carbon pellets to replace them in the bush. They are very low cost, one carton of pellets will last for years. The bottom line, if in doubt change the pellets, we’re talking about 5 cents worth of charcoal here.
My general rule, if I have been using the filter often I change the pellets before I head out. This filter often gets used by groups of survival students and will easily filter enough water for five people over the course of four days. I don’t always change the carbon after trips like that, again, it depends on what we had to filter.
This filter MUST be used with some chemical means of purification or boiling to make the water safe.