Do you mean:
1) -- a filter between the fresh water tank and the pump;
2) -- a filter for pure drinking water at/under the galley sink?
What does your owner's manual say, and if 2) is there a separate mfg. brochure for the filter in your Airstream briefcase?
Have you looked at your pump for a pre-filter on the line coming from the water tank? You need to know the pump's location for winterizing anyway BTW.
How about under the galley sink . . . any filter housing there?
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