I still believe this is an error, and that they should spawn at any fire station with the Water Damage and Flood Mission, irrelevant of Rural or Urban type:
All the missions I listed, excluding the Flooded Mall, have both Rural and Urban mission types (Flooded mall having only urban).
And as DanCoco highlights, you can only have one specialisation on the station – either Water Damage and Flood or Urban/Rural, so you can never actually generate these missions from an appropriate station.
I don’t believe this is deliberate, as it doesn’t follow the same system logic as the other specialisations. When you look at other specialisation types that have the specialisation and either urban or rural type (no Fire Fighting type), they DO spawn if you only have the specialisation and not urban/rural, example:
Light Aircraft Crash in Wildland
This will spawn if you only have the Wildfire specialisation and not rural.
A comparative example:
Small flooding – this will spawn for me with just Water Damage and Flood specialisation
Flooding in a small house, following bad weather – this will not spawn for me with just Water Damage and Flood specialisation
Why does the first mission spawn but the second does not?