Testing a Camping Water Filter

How do we know that these water filters, such as the Lifestraw or the Sawyer Mini, are working properly after long term storage? This Instructable shows a simple, reliable method to determine whether your water filter can properly remove microscopic particles.

Full video here: https://youtu.be/v9SqNZgg7yw

Materials: Water Filter (such as a Sawyer Mini or a Lifestraw), Corn Starch, stainless or glass bowl, cup measure, tablespoon measure, and distilled or RO water

Clean your filter by flushing it with clean tap water per manufacturer's instructions. Sterilize the dirty water bag, hoses, and filter with a mild bleach solution (one capful of bleach or per liter of water). Flush the filter with the provided syringe and clean water until the output in both directions is completely clear. This is simply the maintenance that should be done every time you bring your water filter home from an adventure.

These water filters are designed to filter out 0.1 micron particles - smaller than the bacteria and other nasties that typically make people sick drinking wild water. Cornstarch just happens to be a common material that has 5 to 26 micron particles when mixed with cold water. A water filter should be able to remove 100% of a corn starch solution if it is working properly.

Clean your equipment per manufacturer's instructions - backflushing your filter with the syringe provided with your filter. Sterilize the dirty water bag, filters, and hoses with a mild bleach solution per manufacturer's instructions.

Mix up a solution of 2 cups Distilled or Reverse Osmosis water (use the purest water you can obtain, tap water might work but it is best to use really pure water.), and 1 tablespoon cornstarch. The proportions are not critical.

Reference: Corn Starch Particle Size: https://cameo.mfa.org/wiki/Cornstarch

Water filters use a "dirty water bag" for the wild water you are filtering. You are starting with clean equipment, and you'll clean it when you are done. Add the two cups of corn starch water to the dirty water bag. Some brands have a dirty water bottle or other feature, but the principle is the same.

Filter some of the corn starch water into a clean cup. If it comes out clear, you've successfully filtered out the 5 micron corn starch particles. Any cloudiness indicates your filter is compromised and should be thrown out.

Corn Starch reacts with Iodine, available in any good pharmacy, to make a purple color, easily distinguishable from the red color iodine usually makes in clean water. Drop a bit of Iodine into some corn starch and clean water to see the effects. Drop some Iodine in your output water - the result should be similar to the red color obtained when dropping iodine into regular water. If any purplish or blackish color results, corn starch is detected.

Clean out the corn starch solution by backflushing your filter thoroughly, several times per manufacturer's instructions. Flush all the equipment with clean tapwater. Sterilize the dirty water bag, hoses, and filter with a mild bleach solution (one capful of bleach or per liter of water). Flush the filter with the provided syringe and clean water until the output in both directions is completely clear.

Store your tested water filter per manufacturer's instructions. Depending on the brand, this may involve storing it in a mild saline solution, or allowing it to dry thoroughly. Look up "Long Term Storage" instructions for your particular filter device, procedures vary. Any filter which has not been properly stored is suspect. But properly maintained equipment should last you a lifetime!

You may now be confident that your filter has been tested, and cannot pass 5 micron particles. This should be sufficient to trust that the filter is not damaged and is working properly for your next adventure!

How to I know this test is accurate? The alternative is to replace your expensive water filter frequently. These filters are rated for 100,000 gallons of usage - theoretically enough for several lifetimes of camping. If properly cleaned, cared for and stored, they should be safe to use for decades. This test isn't perfect - it would be better to use a material with particles about 2 microns in size or even smaller, however cornstarch is close enough to the minimum size of these filters that it makes a good home test. Store your filter carefully, never allow a water filter to freeze, and store it in Saline solution (Lifestraw) or carefully flushed and dried (Sawyer) per manufacturer's instructions, and use this test to give you extra confidence that the filter is doing its job. .