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Emerging single‐atom catalysts (SACs) are promising in water remediation through Fenton‐like reactions. Despite the notable enhancement of catalytic activity through increasing the density of single‐atom active sites, the performance improvement is not solely attributed to the increase in the number of active sites. The variation of catalytic behaviors stemming from the increased atomic density is particularly elusive and deserves an in‐depth study. Herein, single‐atom Fe catalysts (FeSA‐CN) with different distances (dsite) between the adjacent single‐atom Fe sites are constructed by controlling Fe loading. With the decrease in dsite value, remarkably enhanced catalytic activity of FeSA‐CN is realized via the electron transfer regime with peroxymonosulfate (PMS) activation. The decrease in dsite value promotes electronic communication and further alters the electronic structure in favor of PMS activation. Moreover, the two adjacent single‐atom Fe sites collectively adsorb PMS and achieve single‐site desorption of the PMS decomposition products, maintaining continuous PMS activation and contaminant removal. Moreover, the FeSA‐CN/PMS system exhibits excellent anti‐interference performance for various aquatic systems and good durability in continuous‐flow experiments, indicating its great potential for water treatment applications. This study provides an in‐depth understanding of the distance effect of single‐atom active sites on water remediation by designing densely populated SACs. [ABSTRACT FROM AUTHOR]