R21.
I should have mentioned in my response that I too have always called it "treated sewage", not that it's a regular topic of conversation, but I have noticed "refined" more recently. I should also have said "sometimes termed refined sewage". Perhaps the use of "refined" is creeping in as part of a drive to make the idea of reusable waste water more acceptable to the public. There's a lot of resistance to it and merely saying that it's "treated' might not be swaying people. The term may only refer to the very advanced form of treatment. Barb will know more about this.
A few examples can be found but, admittedly, not as many as I had expected.
A selection:
From a CIHEAM (Euro) paper on Technologies for water and waste water treatment:
"Nevertheless, the viability of its application must be analyzed in the context of each locality, which may be quite different from the localities where refining and recharging plants have already been installed; and moreover the possibility of growth from the reuse of refined sewage should be analyzed".
From an Australian site sustainabilitymatters.com, listing treatment systems available:
Aqua Engineering DAF (dissolved air flotation) system for treating or refining wastewater, engineered in Europe to EU standards, has been introduced to Australia.
– and this headline from The America's Intelligence Wire:
"It stinks: Overturned tanker was carrying septic waste: Tractor-trailer carrying refined sewage leaks onto roadway."