I have the decanter of endless water, and I got the activation word from Nemelle. When I talk to Ingus's girlfriend, I get the option to say that I have the code and will use the decanter on Ignus. "I'm about to do that" or something like similar.

However, when I exit the dialog with the girlfriend, nothing happens. I can't enter dialog with Ignus, and I don't seem to get any option to use the decanter on him.

Is there something I'm missing?

Never mind. The next time I re-started Planescape the correct dialog options came up when I clicked on Ignus