Science cannot identify the religion concept. Since science gain its popularity with the absence of religion concept. It is human to observe and to look concerning the matter. We already have a country which has to use their own treated waste water in their daily consumption. As the waste water has chemically, physically and biologically altered, and the results, the water is zero defect which can be treated similarly to fresh water, the question is can we use it for wudu'?
The thought bring me to my friend's story. He went to met a doctor to prescribe a mengitis injection before he go to Makkah for Umrah. The doctor, of course a muslim, advice him not to take the shoot as the liquid to prevent mengitis virus might contaminated with un Halal component. The doctor then explain that, it is most likely the works of the enemy of Islam, which wish the muslim doing their ibadah not 100% clean.
I still not found any regulation on the treated waste water that can be used for wudu'. It is only in my thought, before we have a large population concentrated in one region, all water gone through natural purification. Either the waste water will be discharge to the main stream river or seas, or will be circulate in the air. And the water, come to the earth as rain, and then, we used for our daily consumption. The waste water which we see clean and pure (after treated), but then, is the water pure enough to be used to purify yourself before prostrating before Him in our daily solat?