Water Filters and Purification Tablets: What They Miss

Filters and tablets are light, quick and fuel-free, which is why they fill bug-out bags. But each has a gap, and knowing the gaps is what keeps you from getting sick.

Portable filters

• A filter must have a pore size of 1 micron or smaller to remove parasites, and 0.3 micron or smaller to remove bacteria.
• Portable filters do not remove viruses.
• So after filtering, add a chemical disinfectant (iodine, chlorine or chlorine dioxide) to deal with any viruses and bacteria that got through.

Tablets and drops

Follow the package instructions exactly: each product is made for a specific amount of water and contact time.

Product	Kills most germs?	Kills Cryptosporidium?
Iodine (tablets or drops)	Yes	No
Chlorine tablets	Yes	No
Chlorine dioxide	Yes	Yes, if instructions are followed

Iodine cautions: don’t use iodine if you are pregnant, have thyroid problems or are sensitive to iodine, and nobody should drink iodine-treated water for more than a few weeks at a time.

The safe combination

For unknown water in the field: filter, then disinfect. The filter removes parasites (including Cryptosporidium) and sediment, and the chemical handles viruses. When fuel allows, boiling alone does all of it.

None of these methods removes fuel, chemicals or radioactive material. Don’t drink water you suspect is chemically contaminated.