How the KARST filter works
As you scroll, the straw rotates and comes apart, then the view dives into the cut face of its 0.1-micron hollow-fiber membrane. Held at the membrane: sand (100 µm), Giardia cysts (5 µm), and E. coli-class bacteria (2 µm) — all far larger than the 0.1-micron pores. Only water passes through. Nothing bigger than 0.1 microns gets through.
What it is
The cheapest insurance your kit will ever carry.
No pumps, no tablets, no waiting — just lower it in and drink. One straw filters 1,500 liters of untrusted water, catching bacteria, parasites and microplastics up to 0.1 microns.
Specification
- of waterborne bacteria filtered by size exclusion
- 99.9999%*
- rated filter lifespan
- 1,500L
- total weight
- 65g
- hollow-fiber membrane pore size
- 0.1µm
- flow rate
- 600ml/min
- batteries, chemicals or moving parts
- 0
*Based on manufacturer membrane test data (0.1-micron hollow-fiber ultrafiltration; filtration by physical size exclusion).
KARST filters do not remove viruses, dissolved chemicals, heavy metals or salt. Intended for outdoor, travel and emergency preparedness use.
One straw. Different ways to be ready.
Filters waterborne bacteria, cysts and microplastics at 0.1 µm by physical size exclusion.
Single Straw
- →Drink straight from any stream or tap you don't trust
- →Filters waterborne bacteria, cysts & microplastics at 0.1 µm
- →Lasts 1,500 liters
- →No batteries, no chemicals, infinite shelf life
Two-Pack
$19.00 / straw
- →2× KARST Straws
- →3,000 liters of combined capacity
- →One for your pack, one for your car
- →Never caught without a spare
Family Four
$14.75 / straw
- →4× KARST Straws
- →6,000 liters of combined capacity
- →Get one for the whole crew
- →Keep one in every pack, car, kit and home
Before you buy
Questions, answered straight.
What is KARST?
KARST is a personal water-filter straw with a 0.1-micron hollow-fiber membrane. Drinking through it physically filters out waterborne bacteria (99.9999%*), parasitic cysts, microplastics and sediment from streams, lakes or untrusted taps. One straw is rated for 1,500 litres — about two years of one person's daily drinking water — with no batteries or chemicals.
*Based on manufacturer membrane test data — filtration by physical size exclusion.
How do I know it actually works?
Every figure we publish traces to the manufacturer's membrane test data: 99.9999%* of waterborne bacteria and 99.9%* of cysts filtered at 0.1 microns by physical size exclusion. Independent lab verification is scheduled, and we'll publish it the day it lands.
*Based on manufacturer membrane test data — filtration by physical size exclusion.
How does it compare to the best-known straw filter?
Our 0.1-micron membrane is finer than the 0.2-micron pore size common in this category, so it filters by size exclusion down to a smaller threshold. On lifespan we publish the conservative manufacturer-rated bound — 1,500 liters — rather than a marketing ceiling.
What does KARST actually filter?
The 0.1-micron hollow-fiber membrane physically filters out waterborne bacteria, parasitic cysts, microplastics and sediment — anything larger than 0.1 microns. It does not remove viruses, dissolved chemicals, heavy metals or salt. It's built for outdoor, travel and emergency use, not for desalination or chemical spills.
Can it freeze?
A dry, never-used straw is unaffected by cold. Once the membrane has been wet, freezing can crack the hollow fibers and quietly ruin the filter — that's true of every filter in this category. In freezing weather keep a used straw close to your body, and store it fully dry at home.
What if I have a problem with my order?
Reach us anytime through the contact form on this site and we'll help sort it out.
How long does shipping take?
A flat $2.99 covers tracked US shipping on any order — and the Family Four pack ships free. Most orders arrive in 7–12 business days, with tracking emailed the moment it ships.
How long does one straw last?
Each straw is rated for 1,500 liters — about two years of one person's daily drinking water, far longer at trip-only use. There's no shelf-life: store it dry in a kit and it's ready years later. When flow slows permanently, the membrane is spent — that's the signal to replace it.
How do I use and maintain it?
Drink through it like a straw — directly from the source or from a bottle. Five strong sips primes the membrane. After each trip, blow back through it to clear the fibers and let it air-dry uncapped. No chemicals, no backwashing kit, no parts.
In the field
Out where the taps run dry.
