The song “Paris Boulevards” creates a satirical vision of the future, similar to other Brain Contact lyrics (e.g. ‘Texas to Wisconsin’ or ‘Swiss Nightmare’), in which the consequences of climate change are depicted in an exaggerated way.
Here is the key point:
In the year 2100, water is a precious rarity in Paris - but tourists are not complaining about the water shortage, but about the fact that there are no more drinks ‘on the rocks’ (with ice).
This is meant to be ironic and socially critical:
people do not take the existential problems seriously - instead complaining about the lack of luxury (‘no ice in the cocktail’), even though there is literally no water left.