Hi & thanks for asking, my name is Shawn & would like to help you resolve your concern.
How many miles on your Super Duty?
What is your VIN number?
I believe there is a service bulletin on this concern, but I need your vin # XXXXX I can run an oasis report.
I was able to find the technical service bulletin without your vin #, here is the article.
This article supersedes TSB 06-6-5 to update the Service Procedure.
Some 2003-2005 F-Super Duty vehicles built prior to 9/22/2004, 2003-2005 Excursion vehicles built prior to 1/10/2005, and 2004-2005 E-Series vehicles built prior to 9/16/2004 and equipped with a 6.0L diesel engine, may exhibit an intermittent / flickering water in fuel (WIF) lamp. The intermittent condition may be more prominent while turning corners, braking, or during uphill/downhill driving.
Some 2003-2007 F-Super Duty and 2003-2005 Excursion vehicles may exhibit a continuous WIF lamp on, even without the presence of water, due to debris in the reservoir or corrosion on the WIF sensor pins located in the manifold.
Some 2003-2007 F-Super Duty and 2003-2005 Excursion vehicles may exhibit both intermittent / flickering and continuous WIF due to corrosion and the lack of new calibration.
Use the following Service Procedure based upon the customers symptom.
Disconnect both battery ground cables
Raise and support the vehicle
Disconnect the fuel pump, heater, water in fuel electrical connectors from HFCM
Press in the retaining clips and release the fuel hoses closest to the fuel tank
(Figure 3 Number 2).
Remove the screws and the fuel manifold cover (Figure 4).