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In line water filter: match the filter to what you need removed

By the Plain Prepper editors. Updated 2026-10-15.

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Quick answer

An in line water filter sits in a supply line: the 1/4 inch line to a fridge or ice maker, or the hose that fills an RV. CDC says most fridge-type filters use activated carbon mainly to improve taste and smell, not to remove germs. Check the label for NSF certification: Standard 42 covers taste and odor, and Standard 53 covers cyst reduction. Waterdrop's RV filter, for example, is certified for chlorine reduction under NSF/ANSI 42 and should be replaced every 3 months or 1,350 gallons.

Two kinds of in line filter compared

Spec	Waterdrop WD-RVS (RV hose)	Waterdrop 15UC-UF (fridge, ice maker)
Media	Granular carbon, KDF, fluoride media	Ultrafiltration membrane, carbon block, KDF
Rating	20 micron	0.01 micron (ultrafiltration)
Certification stated	NSF/ANSI 42, chlorine reduction	None stated on the product page
Connection	Standard 3/4 in garden hose	1/4 in tubing to fridge or ice maker
Flow	0.5 gpm	Not stated for the UF model
Pressure	20 to 100 psi	10 to 125 psi recommended
Replace	3 months or 1,350 gallons	24 months or 16,000 gallons

Spread evenly, 1,350 gallons over 3 months is about 15 gallons a day; 16,000 gallons over 24 months is about 22 gallons a day.

What different filters remove

CDC's guide to home water filters sorts them like this:

• Taste and smell: activated carbon and filters certified to NSF Standard 42. Most pitcher and fridge filters are this type.
• Parasites such as Giardia and Cryptosporidium: NSF 53 or 58 cyst reduction, an absolute pore size of 1 micron or smaller, or micro, ultra or nanofiltration.
• Bacteria: an absolute pore size of 0.3 micron or smaller, ultrafiltration, nanofiltration or reverse osmosis.
• Viruses: nanofiltration or reverse osmosis.

CDC adds that filters removing germs often do not remove chemicals, and the reverse, so read the label for the specific contaminants listed. You can look up products in NSF's database.

Do you need one?

• Test or check first: CDC says to test your water, or review your utility's annual water quality report, and choose a filter for what is actually in it.
• Wells and rainwater: CDC says to test at least once a year, and whenever color, taste or smell changes.
• Taste is not safety: CDC says harmful germs and chemicals often do not change how water looks, tastes or smells.
• Weakened immune system: CDC suggests talking to a healthcare provider and a water treatment specialist, choosing a system that removes Cryptosporidium, and having someone else change filters.

RV hose filters

An RV inline filter screws between the campground spigot hose and the RV inlet. Waterdrop's guidance for its WD-RVS:

• Flush first to clear loose carbon fines before use.
• Cold water only: Waterdrop says hot water can cause the media to release what it has captured.
• Storage between trips: keep it sealed in a bag with some water inside, somewhere cool, and do not let it freeze; rinse it for a few minutes before reuse.
• Replace on schedule: every 3 months or 1,350 gallons, whichever comes first.

A 20 micron carbon filter improves taste and reduces chlorine. It is not a germ barrier, so follow campground boil notices and see our portable water filter guide for treatment options.

Fridge and ice maker filters

• Exterior filter: Waterdrop says its 15UC-UF can take the place of many built-in fridge cartridges, listing Whirlpool, Samsung, LG and GE models.
• Ultrafiltration: its membrane is rated at 0.01 micron, and CDC lists ultrafiltration among methods that remove bacteria and parasites. Waterdrop's page does not state an NSF certification for this model, so there is no NSF listing to check from that page.
• Connections: the kit includes 1/4 in tubing, adapters and thread tape. Shut off the water supply before connecting and follow the maker's instructions.
• Maintenance: CDC says to change filters on the maker's schedule and to wear gloves, washing your hands afterward.

What to look for when you buy

Questions people ask

What does an in line water filter remove?

It depends on the media; CDC says carbon fridge-type filters mainly improve taste and smell, while ultrafiltration also removes bacteria and parasites.

How often should an in line water filter be replaced?

Follow the maker: Waterdrop lists 3 months or 1,350 gallons for its RV filter and 24 months or 16,000 gallons for its UF fridge filter.

Can an RV water filter be used with hot water?

Waterdrop says no; hot water can make the media release contaminants, so filter cold water only.

Which NSF standard should I look for?

CDC lists NSF 42 for taste and odor and 53 for cyst reduction; check the exact contaminants in NSF's database.

Sources

• About Choosing Home Water Filters, Centers for Disease Control and Prevention
• RV Inline Water Filter (WD-RVS), Waterdrop
• Inline Ultrafiltration Refrigerator Water Filter (WD-15UC-UF), Waterdrop

Sources checked 2026-10-15.