Walk down any RV accessory aisle and you will find filters promising "better water." But better how? Some filters make water taste and smell better. Others are built to catch parasites or bacteria. They are not the same job, and the label tells you which one your filter does. Here is how to read it, using guidance from the CDC and the NSF/ANSI standards that appear on filter packaging.
Start with what CDC says about RV water
CDC's fact sheet Safe RV Water from Tank to Tap says germs can grow in RV water systems, and its filter advice is short and practical: check the label to see which germs or chemicals the filter removes, and replace filters regularly, following the instructions that came with them. It also points out that "many filters designed to improve water's taste do not remove germs."
That last line is the one most RVers miss. A filter can be excellent at what it is designed to do and still not be designed to remove germs.
Taste-and-odor filters versus germ filters
CDC's page About Choosing Home Water Filters draws the same line. It says "filters that remove germs often do not remove chemicals, and vice versa," and that most home filters, such as pitcher and fridge filters, are not designed to remove germs. They mainly use carbon to improve taste or remove metals like lead.
So before you compare brands, decide what you are trying to fix:
- Chlorine taste or odor, or particles in the water: look for a filter that lists those claims.
- Parasites such as Giardia or Cryptosporidium: you need a filter that lists cyst reduction or has a small enough pore size (details below).
- Bacteria or viruses: this takes a different class of filter entirely.
- Lead and other chemicals: check the label for the specific substances named.
What the NSF numbers on the label mean
CDC describes NSF International as "an independent organization that develops public health standards for products" and advises: "Look for an NSF certification on your filter's label to see what the filter will remove." The same page names these standards:
- NSF/ANSI 42: taste and odor. Filters certified to it improve taste and smell.
- NSF/ANSI 53: cyst reduction. Filters certified to it can remove parasites.
- NSF/ANSI 58: reverse osmosis. Filters certified to it can remove parasites.
- NSF/ANSI 62: distillation.
The ANSI Blog's overview of NSF/ANSI drinking water treatment standards adds more context. It describes Standard 42 as covering aesthetic contaminants, "non-health-related, including chlorine, taste, odor, and particulates," and Standard 53 as "intended to help reduce microbiological, chemical, or particulate substances." Standard 401 targets substances at "very low, yet measurable concentrations," and Standard 177 covers shower filtration.
CDC's sample label lists Standard 42 for chlorine taste and odor and Standard 53 for cysts, lead, and other contaminants. You can check a specific product's certifications in the NSF database that CDC links to. If a cartridge's packaging does not mention a standard, do not assume it carries the claim. Look for it on the label or the manufacturer's spec sheet.
Reading micron ratings: absolute versus mean
Pore size is the other number you will see. CDC explains that to judge germ removal you should confirm the pore size is small enough for the germ you are concerned about, and it gives these benchmarks:
- Parasites and amebas: NSF 53 or 58 (cyst reduction), an absolute pore size of 1 micron or smaller, micro-, nano-, or ultrafiltration, or reverse osmosis.
- Bacteria: an absolute pore size of 0.3 micron or smaller, ultra- or nanofiltration, or reverse osmosis.
- Viruses: nanofiltration or reverse osmosis.
The word "absolute" matters. According to CDC, an absolute 1-micron filter catches all particles larger than 1 micron, while a mean 1-micron filter may let some larger ones through. A cartridge that only says "1 micron" without saying which kind leaves the question open.
What each filtration class does
On a separate CDC page, About Home Water Treatment Systems, the agency summarizes the major types:
- Microfiltration (pore size about 0.1 micron, ranging from 0.05 to 5): removes parasites such as Giardia and Cryptosporidium, is somewhat effective against bacteria, and does not remove viruses or chemicals such as lead and arsenic.
- Ultrafiltration (about 0.01 micron): removes parasites and bacteria, is somewhat effective against viruses, and does not remove chemicals.
- Nanofiltration (about 0.001 micron): removes parasites, bacteria, and viruses, and is somewhat effective against chemicals.
- Reverse osmosis (about 0.0001 micron): removes parasites, bacteria, and viruses, and removes some chemicals, including lead, copper, chromium, chloride, and sodium. CDC says to check the label for the specific chemicals a system removes.
Start at the source: test before you buy
CDC notes that harmful germs often do not change water's look, taste, or smell, so testing is the reliable way to know. It also says that if your tap water has no harmful chemicals or germs, you may not need a treatment system at all. For RVers, that means two things from the Safe RV Water fact sheet. First, before connecting to a campground water system, confirm with the manager that the water is safe to drink. Second, when boondocking, fill your tanks from a safe drinking source such as a home tap or other treated water. If your water comes from a private well, CDC recommends testing it for germs at least once a year.
Filters need care too
CDC says filters must be maintained to work properly and to keep germs from growing in them. Change them on the schedule the manufacturer recommends, wear gloves when changing a filter, and wash your hands afterward. Some filters need pre-treatment, so read the instructions that came with yours. CDC also advises that people with weakened immune systems avoid changing filters themselves, because they could be exposed to germs or chemicals trapped in the filter. The same page cautions that whole-home filters that remove chlorine or other disinfectants may allow more germs to grow in plumbing.
Finally, remember that the CDC fact sheet says tap water is not sterile. Do not use straight RV tap water to rinse sinuses (use distilled, sterilized, or boiled and cooled water), to store or rinse contact lenses, to clean wounds, or to fill a CPAP humidifier. Follow the guidance on the sheet for each.
A quick label checklist
- Write down your goal: taste and odor, particles, cysts, or something else.
- Find the NSF/ANSI numbers on the label and match them to that goal.
- If germs are your concern, confirm the pore size is stated as absolute and is small enough for the germ in question.
- Check the label for the specific chemicals the filter lists.
- Note the manufacturer's replacement instructions and follow them.
Where to go from here
If you are ready to compare options, you can browse our RV water filter systems and our replacement filter cartridges. On each product page, check the listed specifications against the checklist above so you know exactly what that filter is designed to do. Questions about matching a filter to your rig? Contact our team at CS@rvwaterfilterstore.com.
