Not sure I understand your question. Gas water-heaters' burner and pilot are positioned in an open-air configuration. There is no "air intake" per se other than to make sure the unit is in a free-air environment. For example, many installations are in closets - but those closets have vents in their walls or doors so air can move freely and the burner/pilot can get all they need.

Have I misunderstood your problem?

Some Whirlpool water heaters had a filter in the bottom.

They were all [supposed to have been] recalled.

Mine was not that model, hence I could not find the intake.

Whirlpool did volunteer, quite eagerly, to send me some free replacement parts for mine even though we don't know if that will fix it or not.