Watkins 31489 Filter Cartridge
Watkins OEM number • 30 sq ft • 5.875″ OD × 10.5″ long
31489 is Watkins's number for this cartridge, not a part you have to buy from Watkins. The filter itself is a 30 square foot cartridge measuring 5.875 inches across and 10.5 inches long, and Pleatco, Unicel, and Filbur all build it. If you read 31489 off an old cartridge or found it in your manual, any of the numbers below drops into the same housing.
Watkins also lists 71825 and 71826 against this cartridge. Different numbers on paper, same filter in the box.
Fitment notes
1-15/16 inch top and bottom openings. Watkins OEM numbers 31489, 71825, and 71826 all refer to this cartridge. Unicel has replaced the C-6430 with the antimicrobial C-6430AM, which it does not ship into Canada; its C-6330 is the same size in 3 oz media against the C-6430's 4 oz. Pleatco also sells this cartridge as the PWK30-4 (4 oz media) and the PWK30-M (Microban), both the same fit.
What to buy instead
Replacements for the Watkins 31489
Each button searches Amazon for one of the numbers this cartridge is sold under. The OEM version is usually the most expensive of the set and the aftermarket versions are the same physical filter, so it is worth checking all of them before you order.
Every number for this filter
| Brand | Part Number | Type |
|---|---|---|
| Watkins | 31489 | The number you searched |
| Pleatco | PWK30 | Aftermarket equivalent |
| Unicel | C-6430 | Aftermarket equivalent |
| Filbur | FC-3915 | Aftermarket equivalent |
| Hot Spring | 31489 | Other OEM number |
| Watkins | 71825 | Other OEM number |
| Watkins | 71826 | Other OEM number |
Full specs, the cartridge diagram, and the complete compatibility list live on the PWK30 cartridge page. You can also see every 5.875″ × 10.5″ cartridge if you are checking a measurement rather than a part number.
Equipment that uses this cartridge
Looking for a different model? Browse every Watkins model we cover.
Frequently Asked Questions
What filter replaces the Watkins 31489?
The PWK30 replaces it directly, and so does every cross-reference for it: C-6430, FC-3915. All of them are the same 30 sq ft cartridge at 5.875" outer diameter and 10.5" long. Buy whichever is cheapest at the time with solid recent reviews. The same cartridge also shows up as Hot Spring 31489, Watkins 71825, Watkins 71826, so those are not different filters either.
Is the Watkins 31489 the same as the PWK30?
Yes, physically the same filter. Watkins 31489 is an OEM number, meaning it is the code Watkins put on the cartridge that shipped with the equipment. Watkins does not manufacture cartridges. Pleatco, Unicel, and Filbur do, and they sell the identical part under their own numbers at a lower price. Match the dimensions against your old cartridge before ordering and you are covered.
Do I have to buy the Watkins version?
No. Nothing about the housing requires an OEM-branded cartridge, and the warranty on your equipment is not voided by using an aftermarket filter that meets the same spec. The reason to buy OEM is convenience, not performance. The reason not to is price, which is often a meaningful gap for an identical part. What matters is that outer diameter, length, and end-cap style all match.
What size is the Watkins 31489?
5.875 inches in outer diameter, 10.5 inches long, with 30 square feet of filter media. Both measurements need to land within about an eighth of an inch, and the end caps have to match so the cartridge seats correctly when you close the lid. Measure your old one rather than trusting a number that has worn off the label.
Last verified August 2026