The Shell Water Detector Capsule is the industry standard test for monitoring the level of free or dispersed water in jet fuel. It is used in conjunction with a syringe that draws 5 ml of fuel through the capsule.
If the paper inside the capsule does not change color from yellow to green, the water content of the fuel is below the IATA recommended water content limit of 30 ppm and the test is passed.
Saturated green means the fuel contains more than 30 ppm water and the test is classified as a fail.