PureFlow makes an emergency water filter straw. It's a passive mechanical filter, so it needs no power, no chemicals, and no heat.
The company's own framing is that most filter straws on the market were designed for weekend hikers, and that a grid-down event is a different problem with different math.
Whether you buy that framing or not, the mechanism is worth understanding, because it's the whole product.
Water gets pulled through four stages.
Stage one is a coarse screen. It catches sand, mud, and visible debris, which protects everything behind it.
Stage two is medical-grade PP cotton. It takes out fine sediment and micro-particles.
Stage three is a flow stabilization layer. It evens the pressure across the membrane. That sounds like a footnote. It isn't. It's the reason a kid or an older adult can pull water through it without giving up.
Stage four is a hollow fiber membrane at 0.01 microns. This is where the filtration happens.
It removes 99.99% of bacteria and 99.99% of protozoa, which covers E. coli, Salmonella, cholera, Giardia, and cryptosporidium.
It also blocks microplastics.
Those are the organisms behind most acute illnesses from contaminated water.
For context, common hiking straws filter at 0.2 microns (LifeStraw) and 0.1 microns (Sawyer).