I'm currently in my last year of my master in environmental engineering and I'm strongly thinking about doing a PhD afterwards.
I'm looking around for possible supervisors working with research topics that I'm interested in (especially micropollutants removal from water), but I don't know how to assess their and their research group reputation. What would be the best method to assess that?
Also how early is it acceptable to send an email to inquire about a possibility to conduct a PhD project with them, especially if they work in a different university and thus know nothing about you?