I have one and used it on a trip this summer in Arizona. Worked great the 1st day when the river water was clear on the Verde River. However it rained that night and the river rose and kicked up a lot of sediment. Filled two bottles using the provided filter and a bandana and it still looked like chocolate water. In those conditions the pen will not work. I resorted to 2% iodine that I had in my 1st aid kit, 5 drops per 32 oz and let it sit for an hour and then drank. The water was gritty, but had no ill effects. Bottom line: the pen worked great for me, but I am glad that I had a back up for cloudy water. I will be using it again.
Mike
