If you hike or backpack in areas that have large amounts of decaying vegetation, like the forests of North America, you’re going to come across natural water sources that have a sickly red, orange, or yellow color. The tea-like coloring is caused by tannins that have leached out of the trees, grasses, and leafy plants, and into the local water supply. This coloring is harmless and the water can be filtered or purified by regular means for human consumption. While it’s aesthetically displeasing and may impart a slight bitterness to the water, tannins do not pose a health or medical issue.
Some water filters can partially remove tannins from the water, particularly those with an activated carbon component like the Katadyn Hiker Pro, which can make the water more palatable. The MSR MiniWorks Ceramic Filter can also remove tannins, but must be brushed (cleaned) occasionally to restore its normal flow rate. However, tannins will reduce the lifetime of most hollow fiber filters such as the Sawyer Squeeze, the HydroBlu VersaFlow, and the Katadyn BeFree unless they are backflushed more frequently.
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