RV water filter finder

The questions go in order. Nothing is sent anywhere.

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Garden hose thread, and the leak people actually get

A campground spigot, a garden hose coupling and the city water inlet on an RV all present the same standard thread, and Apex Flow Solutions publishes what it is: 3/4 inch - 11.5 NH, garden hose thread. It is a straight thread, so it seals on a rubber washer at the face and not on the threads, and it takes no thread sealant.

3/4 inch NPT is a different thread. Its outside diameter is 1.050 inch against garden hose thread's 1.0625 inch, close enough that the two engage part way and then cross, which damages the threads and causes a leak. NPT needs an adapter and thread sealant, and the two threads never screw together. An adapter from garden hose thread to 1/2 inch NPT is what closes the gap when a filter has pipe ports and the run is hose.

The inlet makers state their own ends. Aquor publishes its RV city water inlet as 1/2 inch NPT female behind a 3/4 inch GHT male face, and RecPro publishes its city water fill as 3/4 inch outside and 1/2 inch inside.

Inline filter or housing

An inline filter screws onto the hose or the inlet and is replaced whole, with no housing to open. A housing holds a cartridge, and only the cartridge is replaced. The inline filters in this tool's record are the ones the makers publish a figure for, from the Shurflo city water entry filters with their 3/4 inch garden hose ports to the Waterdrop and RVGUARD hose-end filters.

The housings are bought by their format, which is the size of the cartridge they take. The makers that publish a housing and its format are Pentair Pentek with the Slim Line series, Pentair Shurflo with its Waterguard housing and complete kits, and Clearsource with the canisters on its Premier and Ultra systems.

The cartridge formats, and the stops that matter

The format is the fit. You buy a cartridge by its measured diameter and length and by the end cap it takes, and the makers publish a fixed set of formats, not an open one. These are the formats in the record:

The three hard stops

A 2.5 inch cartridge is not a 4.5 inch cartridge. The two are different formats, and a slim line cartridge floats and bypasses in a Big Blue housing rather than sealing. A 20 inch cartridge never goes in a 10 inch housing: the nominal length is the housing size, not a cartridge that fits any bowl. And the end cap type has to match, double open end or single open end, or the cartridge will not seat even at the right diameter and length.

A nominal 10-inch cartridge is about 9.75 to 9.88 inches long, because the housing end caps and the O-ring take the difference. Measure the actual cartridge rather than the size it was sold as.

Why no maker cross-references a cartridge to another maker's housing

Within one diameter family, cartridges interchange across housing brands as long as the end cap type matches, and the record's rule says exactly that. What no maker publishes is a cross-brand part-number cross-reference, so this tool never states that a named cartridge fits another maker's named housing. It states the format, which is what the makers publish, and leaves the part number to the housing you own.

Which end is the inlet

The arrow on the filter body points in the direction of water flow, and every maker that prints one says to follow it. Fitting a filter against the arrow puts the water through it backwards.

When the water runs slow after fitting

The low flow class of inline filter is rated at about half a gallon per minute, which is enough for a tap and slow for a tank. On an RV that fills its fresh water tank through the filter, choose by flow rate rather than by microns alone, because a fine filter that trickles turns a fill into a wait.

Winter, and what every maker says about it

Every wet filter in the record has to come out of the cold, and the makers agree on one thing: protect it from freezing, and do not push antifreeze through it. The rules, maker by maker:

• Camco. Protect the filter from freezing, do not winterize with antifreeze of any type, and store it capped in a refrigerator
• Hydro Life. Do not allow antifreeze to flow through the filter; take the filter out of the coach and put it in the winterizing bypass hose that came with the system, and store it in a sealed bag with water covering it, not colder than 35 degrees F
• Pentair Pentek. Protect the housing against freezing to prevent cracking of the filter and water leakage
• Waterdrop. Put the filter in a sealed bag with some water left in it and keep it somewhere cool such as a refrigerator, and do not freeze the filter
• Clearsource. If the system will not be used for a month or more, unscrew the canisters, empty the water and remove the elements to dry storage in sealed bags

Where to go next

The filter sits in the same water system as everything else, and the rest of the system has its own pages. Winterizing the plumbing works through the whole system, filter included. A water pump that will not prime covers the supply side when a filter is fitted. And the water heater anode rod finder is the other part of the fresh water system that gets replaced on a schedule. The parts page lists the filter housings and cartridges alongside the rest of the water system. Fitting a housing is a job a mobile technician can do, and the directory finds one by state.

By OriginRV. Last reviewed on Nov 2, 2026.