Developing a water-soluble supramolecular system for the detection and removal of Hg is extremely needed but remains challenging. Herein, we reported the facile construction of a fluorescent supramolecular system () in 100% water through the self-assembly of carboxylatopillar[5]arene sodium salts () and diketopyrrolopyrrole-bridged bis(quaternary ammonium) guest () by host-guest interaction. With the addition of Hg, the fluorescence of could be efficiently quenched. Since Hg showed synergistic interactions (coordination and Hg- cavity interactions with and , respectively), crosslinked networks of @Hg were formed. A sensitive response to Hg with excellent selectivity and a low limit of detection (LOD) of 7.17 × 10 M was obtained. Significantly, the quenching fluorescence of @Hg can be recovered after a simple treatment with NaS. The reusability of for the detection of Hg ions was retained for four cycles, indicating the could be efficiently used in a reversible manner. In addition, the could efficiently detect Hg concentration in real samples (tap water and lake water). The developed supramolecular system in 100% water provides great potential in the treatment of Hg detection and removal for environmental sustainability.