I will second Naples ...

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I will second Naples Florida and Collier County Florida in the US as being above 90% in their water reuse program, which is constantly expanding.  A recent report:

https://legistarweb-production.s3.amazonaws.com/uploads/attachment/pdf/166785/2018-03-16_FINALReclaimed_Water-Summary_Report.pdf

In Southwest Florida about one third of the wastewater is reused. However, in some counties within that area over 90% of the wastewater is reused:

https://www.sfwmd.gov/our-work/alternative-water-supply/reuse