A conjugated polymer with ratiometric absorption, namely poly-deca-4,6-diynedioic acid (PDDA), has been developed for the naked-eye detection of zinc ions (Zn²⁺) in water samples. This probe possesses both excellent Zn²⁺ selectivity and great sensitivity based on the absorption ratio change of PDDA upon the addition of Zn²⁺. The water-soluble PDDA is able to detect Zn²⁺ in the pH range of 6.4–10.4, and the detection of Zn²⁺ by PDDA is not affected by the presence of other metal ions and anions. PDDA appears yellow with a maximal absorption at 468 nm, and shows a significant color change from yellow to orange when Zn²⁺ reaches 1.0 mg/L (the national standard of China), and to pink color when Zn²⁺ reaches 3.0 mg/L (the World Health Organization recommended level). Notably, PDDA also serves as a reusable adsorbent to effectively remove Zn²⁺ in water samples, with an average recovery rate of 97.75% for PDDA and a removal efficiency of 84.54% for Zn²⁺. PDDA herein represents an unprecedented probe integrating the rapid and accurate naked-eye identification of Zn²⁺, as well as the efficient and sustainable removal of Zn²⁺ in water media.