ABSTRACT Developing water‐stable organic room‐temperature phosphorescence (RTP) materials remains a formidable challenge due to water‐induced quenching. Herein, we present a counter‐intuitive strategy to achieve water‐enhanced ultralong RTP via the in situ encapsulation of carbonyl‐based guests within a rigid hydrogen‐bonded organic framework (HOF). Unlike conventional systems where water acts as a quencher, we demonstrate that water molecules function as pivotal structural reinforcers. Mechanis