Application of Co-Kriging method to estimate water hardness with secondary variable PH in West Surabaya

Surabaya, one of Indonesia’s largest cities, faces significant challenges due to its rapid population growth, especially in West Surabaya. Access to clean water is critical for this population, essential for sanitation and hygiene per Indonesian Ministry of Health regulations. This study estimates water hardness in West Surabaya using pH as an indicator, contributing to the Sustainable Development Goals (SDGs), particularly goal 6, “Clean Water and Sanitation.” Water quality assessments involve chemical, physical, and biological tests. This research focuses on water hardness and pH, utilizing Co-Kriging, which uses cross-correlation between variables to enhance estimation accuracy. The study evaluates semivariogram models (exponential, spherical, and Gaussian) to find the best fit for estimating water hardness. Previous research shows Co-Kriging provides more accurate estimates than other methods. This study fills a gap by applying Co-Kriging to estimate water hardness in West Surabaya using pH as a secondary variable. The findings indicate that the Gaussian semivariogram model is the most accurate, with an MSE of 1068.9 and a MAPE of 18.87%. West Surabaya’s water hardness averages 146.4 mg/L, classifying it as clean water, with an average pH of 7.7143, indicating slightly basic water. The study recommends increasing observation points and examining factors like total dissolved solids (TDS) and electrical conductivity for future research. This research helps policymakers and environmental agencies in monitoring and managing water quality, supporting public health and environmental sustainability in West Surabaya.