The bacterial taxa found collectively in monochloramine treated and control samples were very dissimilar (Fig. 4 and Supplemental Fig. 3). Pairwise comparisons between treated and control samples showed distinct assemblages with a Morisita–Horn Index (MHI) below 0.09 (Supplemental Fig. 3). Fig. 4 summarizes these data by pooling the libraries generated for each month in the treated and control building, whereas Supplemental Fig. 4 shows data comparisons for all samples. While MHI was very high within the two buildings for the May and June time points, treated and control water samples collected in July had slightly reduced MHI (Fig. 4). However, MHI did not decrease to the level of the com-parison between the treated and control samples, showing that monochloramine treatment still caused an alteration in the micro-bial community (Fig. 4 and Supplemental Fig. 3). A similar result was seen when comparing all samples individually with high MHI when comparing individual samples from within chloraminated or control building samples (Supplemental Fig. 3).