Water In Fuel Warning Light (Diesel)
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1997 GMC Savana Special, 1997 GMC Savana Camper Special, 1997 GMC Savana, 1997 Chevrolet RV Cutaway, and 1997 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
As a bulb check, light will come on when ignition is turned on. If no problem exists, light will go out when engine is started. If light stays on at any time, excessive water in fuel filter is indicated. Service filter immediately.