In a 2002 staff interview with Nintendo Dream, director Yoshiaki Koizumi revealed that FLUDD was inspired by his memories of playing with water guns as a kid, an image that he recalled upon first using the analog L & R triggers on the GameCube's controller. Series creator Shigeru Miyamoto further explained that the concept behind FLUDD was controversial among Nintendo's staff due to Mario not being widely associated with these kinds of tools, though Luigi's use of the Poltergust in Luigi's Mansion ultimately served as a precedent in the concept's favor.

In the same interview, Takashi Tezuka stated that Nintendo went to great lengths to keep FLUDD from resembling a firearm, both due to Koizumi finding a water gun "too simple" and due to concerns that guns (or anything that audiences may interpret as such) would be inappropriate for the franchise's public image. The "weird backpack thing" that FLUDD ultimately ended up as addressed both concerns at once, with Koizumi likening it to firefighting equipment and "a [plastic] bottle water rocket toy."