On Friday, February 13, Xi Bai successfully defended her excellent thesis, “The Role of Microbial Ecology in the Functioning of Slow Sand Filters for Drinking Water Production.” Her research significantly advances our understanding of slow sand filtration and supports drinking water companies in ensuring safe drinking water, both now and in the future. Her co-promotor, Inez Dinkla of Wetsus, and I are very proud of her and wish her every success in her future career.