Introduction: The copper content in natural waters usually range from 0.2 to 30 μg/L. The higher concentrations are habitually found in industrial effluents and other contaminated waters. Methods: This work develops the spectrophotometric method of determination of copper (II) microgram amounts with a new reagent - sodium salt of 4- phenylsemicarbazone 1,2-naphthoquinone-4-sulfonic acid (L), used as a ligand for a new coordination compound of copper (II). The complex formation is accompanied by color change, allowing use of this property for quantitative determination of copper (II) ions in various objects such as: alloys, superconducting ceramics and tap water. The determination of copper (II) ions has been carried out by voltammetric and spectrophotometric methods. Results: The complex of composition CuL is stable within the pH range from 5.74 to 6.51. Its stability constant is logβ = 4.53. The molar absorption coefficient of the complex has been found. Both methods give the same concentration of about 0.0400 mg/L of copper (II) in tap water, ceramics, and alloys. The detection limit of the spectrophotometric determination of copper (II) ions in the presence of the main metal ions in tap water is 0.012 mg/mL. Conclusions: The advantages of this method are the simplicity of the synthesis of reagent, its ease of recrystallization from water-ethanol solution, and stability in the crystalline state.