Ordinary kriging is one of the geostatistical techniques used for spatial prediction on a spatially distributed random plane. Ordinary kriging is a linear unbiased estimator which is part of a semivariogram system of equations that minimizes errors of variance in estimating mineral resources. The semivariogram model shows optimal results in the estimation using the least square method, the effective minimization method smoothes the data points against the curve on a semivariogram graph, the least square makes the size error efficient in the semivariogram model and has been proven to be effective in reducing errors in the semivariogram model in the case of laterite nickel deposits. at PT. Vale Indonesia Tbk. Thus, conclusively the prediction of unsampled Ni content results is very accurate. This is indicated by the lowest root mean square error (RMSE) in limonite in the exponential model, saprolite in the spherical model, and bedrock in the gaussian model. The greatest value of Ni content in this study was in the saprolite layer.

Geostatistik merupakan suatu metode dalam ilmu statistika yang digunakan dalam distribusi keruangan. Geostatistik memuat  korelasi antar sampel data yang di dalamnya terdapat variabel teregionalisasi yang disebut kriging. Kriging mampu memberikan taksiran yang sangat baik dengan meminimalkan variansi kesalahan melalui korelasi antar sampel titik bor. Identifikasi model dalam semivariogram diperoleh model terpilih yaitu model eksponensial untuk lapisan limonit, model spherikal untuk lapisan saprolit, dan model gaussian untuk lapisan bedrock. Model tersebut terpilih yang menunjukkan nilai RMSE untuk lapisan limonit sebesar 0.13, untuk lapisan saprolit sebesar 0.52, dan lapisan bedrock sebesar 0.15. Penghalusan model pada kurva dideteksi oleh ordinary least square (OLS) yang meberikan hasil yang sangat baik. Hal ini dibuktikan dengan model yang sudah mendekati sill secara asimtotik dan range sama dengan jarak dimana model kurva sudah mendekati 95% maksimum. Dengan demikian, studi ini secara meyakinkan membuktikan bahwa dengan pemilihan model yang tepat dalam semivariogram eksperimental maka memberikan hasil prediksi kadar Ni yang baik dan akurat.

The increasing demand for drinking water demand in Indonesia is mainly determined by the rapid population growth. In overcoming the issue, the development and rehabilitation of water supply system are necessary. The tariff or rate of water is a price assigned by water authorities on water supplied and distributed to their customers through the pipe network. A tariff is not only to recover the full costs of its supply and production, but also to incorporate the operation costs. Hence, it establishes the continuity of the water supply in the future. This research aims to determine tariff or water rate in HIPPAM System with the case study at Salawaty District – Sorong Regency. The tariff should be adjusted to the ability to pay of customers, and it is based on the income and the amount of water paid in a month. Besides, the next parameter is the willingness to pay that can be obtained from the customer survey. The results show that the majority of customers are willing to pay the water rate at the low price of IDR 1500/m3. On the other hand, the research suggests that the most appropriate tariff in the study area is IDR 2456,1/m3. This tariff is assumed to be able to guarantee the continuity of the drinking water supply system in the future. Keywords: tariff, water supply, HIPPAM, Salawati District, Sorong Regency