A novel reversible colorimetric chemosensor based on a water-soluble polymer containing rhodamine receptor pendants has been developed. The chemosensor exhibited high sensitivity and selectivity to Cu²⁺ ions with a short response time in pure aqueous solution, and the results could be monitored directly by the naked eye. The detection limit was 3.6 × 10⁻⁷ M with UV-vis absorbance experiment. The absorption intensity of P(HEA-co-RhBBA) for Cu²⁺ remained unaffected over a wide pH range of 4–10. In addition, low-cost test strips were fabricated using P(HEA-co-RhBBA) for convenient and efficient detection of Cu²⁺ ions.