There are 2 types of Karl Fischer titration: one is Volumetric, and the other is Coulometric.

Although the endpoint of the reaction is marked by a persistence of the yellow color (iodine color), using the eyes is not very accurate. Both methods use bipotentiometric titration to measure the amount of iodine consumed by the water.

Bipotentiometric titration is simply monitoring the extent of reaction by measuring changes in electrical conductivity of the reaction solution.

The difference between them is primarily in the way the iodine is generated:
In volumetric titration, the iodine is included with the reagents;
In coulometric titration, the iodine is generated at an electrode.

Which one the user chooses depends on:
1. The method they are following or personal preferences;
2. The titration equipment they currently have in the laboratories;
3. The water levels in the sample, generally:
Volumetric: 0.1 - 100% water
Coulometric: 0.001 - 0.1% water