Water Filters vs Purifiers vs Tablets: Which Do You Need?

Filters, purifiers and tablets all make water safer to drink, but they do not all remove the same things. The right choice depends on where you are and what is in your water. Here is a plain comparison.

What can be in untreated water

Bacteria such as E. coli and Salmonella, protozoa such as Giardia and Cryptosporidium, and viruses can all make you sick. Viruses are far smaller than bacteria and protozoa, so many common filters cannot remove them. Chemicals and heavy metals are another category that most basic filters and tablets do not address.

Filters

Most portable filters use hollow-fiber membranes with pores small enough to block bacteria and protozoa. They are fast, taste-neutral and require no waiting. Most do not remove viruses on their own. In North America and other areas where viruses in backcountry water are less common, a filter is often considered sufficient for hiking.

Purifiers

A purifier removes or inactivates viruses as well as bacteria and protozoa. Some use a very fine filter, some use chemical or ultraviolet treatment, and some combine methods. If you are traveling internationally or dealing with flooded areas or sewage contamination, a purifier is the safer choice.

Chemical tablets

Tablets, often chlorine dioxide, are light and cheap, which makes them an excellent backup. They treat bacteria, viruses and, depending on the product and wait time, protozoa. The trade-offs are the waiting time, which ranges from about 30 minutes to several hours for some pathogens, and a slight taste. Always follow the instructions on the package.

Side-by-side

Method Bacteria Protozoa Viruses Speed Weight

Filter Yes Yes Usually no Fast Light to medium

Purifier Yes Yes Yes Fast to medium Medium

Tablets Yes Depends on product and time Yes Slow Very light

Always check the specific product's stated ratings rather than relying on the category alone.

What none of them do

Most filters and tablets do not remove chemical contamination, such as fuel, pesticides or heavy metals. If your water source may be chemically contaminated, find another source.

Our recommendation

• Day hikes and home outages: A filter with tablets as backup
• International travel or flood response: A purifier or filter plus tablets
• Ultralight or emergency kits: Tablets, plus a filter if weight allows

Next step

Compare water treatment products.