Some years back, I've seen this anime at a friend's place ...
I was about a city in the future where "pure" (naturally born) humans were only a few and the rest were created artificially, I don't remember if this was the case about the entire world or just located in one geographical point.
What I do remember is that the city was ruled by a council of old men (naturally born humans), that one day decided to give the artificially created humans the ability to procreate and thus to actually kill the entire remaining naturally born humans.
Probably it was about the entire world...
And I think I'm getting a bit confused here but, I think in this anime there was in the 1st episode a car that wasn't using wheels like any other, but was hovering instead.
And this anime didn't have the gloomy feeling like ergo proxy... it was rather busy and filled with life (the city at least)...
It could be that the water level had risen but I'm not sure...