Well then. I'll set the record straight.

Water supply is taken from the oceans and filtered/purified to be drinkable. There is enough water from lakes and oceans and ice to sustain the world, considering that today, we're sustaining and we only inhabit under 30% of the space on Earth today with 7 billion people. Considering the population has doubled to 14 billion, we'd be sitting at under 60% total occupied where the Earth is 70% covered in water, we'd still have a surplus if things are looked at in that perspective (not real math but good enough to convey the point). Combine that with recycling and yes, water is a non-issue. Food is also massed produced and since a good chunk of the population is more machine than man, not everybody requires food.

Resources that have been exploited and depleted have been replaced with effective alternatives and artificial materials.

Considering that the entire population ISN'T in LA today, then there's no reason to suggest that some massive exodus to one spot occurred at any point either. People like space, nations like boundaries and not everywhere in a city is home to individuals. Industrial sectors, economic centers, political centers aren't the same as residential centers. Lots of space is devoted to manufacturing, recycling and powering the massive platforms surrounding the Earth.

Now, regarding this argument that is brewing. I understand the skepticism, but please remember that this setting is still a work in progress and others are free to provide their input to help flesh out the world. We don't have the ability to look five thousand years into our future and see how Earth and Humanity is going to end up so this setting is fantasy and doesn't need to be realistic. I'm explaining at a capacity to make one think 'I can picture this' without having them go into the physics and logic behind it since there shouldn't be. How would Coruscant in Star Wars be logical? And that's like a super-sized version of this setting's Earth. Please, everybody, read other's posts neutrally to not get the wrong idea.