Re: thermal de-sal
"If you already have thermal power stations, then even after the 2nd or 3rd stage turbines the steam still has heat to help boil off seawater, and as you need to cool the steam off anyway the combined power and water plant can work out cheaper overall than RO."
That's a consideration, yes, and I'm sure power plant designers are keen to extract every last bit of heat out of their boilers (or at least until Diminishing Returns kicks in), but I think this will work only if the power station is close to a source of salt water. Otherwise, the pumping costs will likely tip it below break-even. Plus there's the issue of cleaning up the byproducts over time.
"The nice thing about TSE is that as the city grows, you get more of it. You can see this in action in Oman where the trees along the side of the highways reach further out of town every year."
You would think that your sewage treatment costs would rise along with the population. You'll need to increase your capacity so that you can treat more sewage at a time, and this may also involve additional capital expenditures (more tanks, etc.). How will does TSE scale with population growth?