Sewage is different, because it has a high concentration of WC water (urine), which in turn contains high level of hormone supplements (contraception). Some of the problem is, that these drugs can eventually find their way to fresh water.

The standard scientific (chemical) process is the mechanical separation and dilution mentioned, but there is no evidence that there is a safe level of hormone that can be absorbed daily. Not unlike DDT: actually hormones were cited as evidence during the fight for the ban. However, there is scientific evidence of sexual mutation in creatures living in water (frogs, fish etc. -- though many other things could be blamed for this, but none rule out the above)

If recycled water will be passed back to producer, then cycle will be created. Cycles are vital for life.

If a virus will find way to bypass all filters and return back to human body, then we will have huge problem.