Many (maybe most) waste water treatment plants produce potable water. That’s what they are for. They take sewage and make it safe for the environment (which is to say it is safe to drink). I’m sure this is simply a bureaucratic regulatory thing.
In industrial buildings that require a waste treatment plant, the waste water leaving the plants can be drank from the discharge pipes (at least initially). It tastes fine.
There is a cost for the energy plant and the energy, but there is an abundance of saltwater. When one drills for oil/natural gas, the oil companies have to deal with saltwater.
Just boil it (using de-salination process), and one has fresh water...
That is my tangent - start producing fresh water in dry areas using de-salination plants...
I worked a construction job with my pop when I was teenager in the early 90’s.
There was quite a few tomotoe plants growing around the water plant.
My dad told me it was the seeds picked up by seagulls or blown by wind from the processing pools.
I don’t know if he was messing with me @ the time, but it sounded reasonable.
Llama