A’yun, Qurota, et al. “Analysis of Hardness Level and PH of Drilled Well Water in Semin Village, Semin District, Gunungkidul Regency”. Jurnal Biologi Tropis, vol. 23, no. 3, July 2023, pp. 310-5, doi:10.29303/jbt.v23i3.5086.