One knock on the Grayl design is the possibility of cross-contamination because the outer container used to scoop water could drip unpurified water near the top of the bottle when you're drinking or pouring it. From what I've seen, Grayl redesigned the top of the Geopress (24 oz.) to help eliminate this potential problem; however, the Ultralight (16 oz.) appears to maintain the original design. I could see where cross-contamination could happen if not careful, especially when using the Ultralight design.
I'm probably over-thinking this. I imagine this could be a potential problem with any design where the filter and container are incorporated into a single unit such as the Katadyn Befree, Sawyer Squeeze, etc.
Last edited by CoalCracker; 08/22/21.
