Originally Posted by
balto charlie
... I have thought about the Steripen. I thought cloudy water was an issue with this device.
....
Yes, it is. The UV rays make the microbes non-reproduceable or kill the microbes, but the UV is light and light travels through clear water a lot easier than cloudy water. And water does not have to be very cloudy at all for a UV treatment device to fail.
An excellent example of an ideal usage for this device is like Djb suggested when he commented that he used one on untrustworthy tap water in developing countries.
A lot of lakes and streams in conifer forested areas can have a lot of dissolved tannins, I am assuming that the tannins can also absorb UV light and limit how well a UV treatment device works, but I have seen no research on that topic. I would simply avoid relying on a UV device if the water looks like weak tea. I have drank a lot of tannin laden water in Northern Minnesota, but that was filtered or boiled water.
I do not know much about blue green algae, but that is an occasional concern, including in some wilderness areas and nothing that campers carry can make that safe. But, it has been quite rare to date, so I would not worry about it unless you become aware that it is an issue where you might travel.