The Yogyakarta-Sleman Groundwater Basin has an important role in providing water resources for people of Sleman Regency, Yogyakarta City, and Bantul Regency. If it is not managed properly, excessive groundwater utilization can reduce the quality and quantity of groundwater. This study aims to determine the level of groundwater utilization in the Yogyakarta-Sleman Groundwater Basin. The method used is the calculation of dynamic groundwater and water utilization according to the Indonesian National Standard (SNI) number 19-6728.1-2002. The results showed that the trend of total groundwater utilization from 2013 to 2018 has increased in Sleman Regency, Yogyakarta City, and Bantul Regency. However, when viewed from the level of groundwater utilization, Sleman Regency, Yogyakarta City, and Bantul Regency are dominated by low utilization rates, while the very high utilization rates in Sleman Regency are in Godean and Gamping Districts. The utilization rate is very high in the city of Yogyakarta, located in Umbulharjo District. While the level of utilization is very high in Bantul Regency, in Imogiri District. Thus it can be concluded that the level of groundwater utilization in the Yogyakarta-Sleman Groundwater Basin area is quite diverse, dominated by the low category but there are several sub-districts in the very high category, so that the groundwater utilization zone in CAT Yogyakarta-Sleman still needs control, so that it can be sustainable and utilized in the long term. Keywords: groundwater basin, groundwater use, index of groundwater use

Water-scarce areas can be identified from geology, meteorology, water installations, and drought conditions in the area. All of these aspects can be found in Kulon Progo Regency. The aim of this research is to identify water scarcity areas in Kulon Progo Regency and to determine priorities areas for building up some deep wells. There are four parts of the method that used in this study, there are water scarcity areas from the geological aspect interpreted based on geological, hydrogeological, and groundwater basin  maps, meteorological aspects using the water balance method and drought index, distribution water installation analyzed from PDAM data, and drought information collection from interview. Based on a study on the identification of water scarcity areas in Kulon Progo Regency with geological and hydrogeological parameters, meteorological drought, PDAM and SPAM, and Interviews, it was found that 181 hamlets that having water-scarce in 35 villages in 11 sub-districts both covering areas that can be drilled and cannot be drilled. The number of water-scarce areas selected for groundwater drilling is 104 hamlets. The number of water scarcity areas in 1st priority is 37 hamlets, there are 21 helmets for 2nd priority, and 46 hamlets for 3rd priority.

The number of unregistered artesian wells increases every year in the northern slopes of Bromo Volcano, Pasuruan. Artesian wells are used for domestic needs and agricultural irrigation but are not followed by environmentally sound groundwater use. The purpose of this study is to assess the potential for groundwater, groundwater use, wasted groundwater, and recommendations for groundwater management.  The groundwater potential was obtained by measuring the depth of the groundwater table, piezometric surface of artesian wells, and geoelectrical data. Water uses were obtained from calculations based on the Indonesian National Standard. The amount of wasted groundwater was obtained by comparing the groundwater potentials, groundwater uses, and groundwater discharges from unregistered artesian wells. Water transfer was assessed by selecting unregistered artesian wells with discharges able to fulfill the water demands of each village. Groundwater in the Sub-Districts of Gondang Wetan and Winongan has high potential consisting of 1 unconfined aquifer group and two confined aquifer groups. Gondang Wetan and Winongan Sub-Districts are characterized as wasting groundwater potential through unregistered artesian wells. The discharge flow of unregistered artesian wells exceeds the water needs (>100%) in Winongan and Gondang Wetan Sub-Districts. Groundwater can be managed by water transfer, closure of artesian wells, and regulation of artesian wells use. Water can be transferred to areas not covered by Artesian wells in 20 villages. The number of artesian wells used for water transfer is 20 with a discharge of 5-20 liters/s.

Merapi Volcano, which differs from volcanoes in other climates due to its location on the Indonesian Maritime Continent influenced by ENSO, ICTZ, and Moonsons, plays an essential role as a source of groundwater for the surrounding population. Some problems associated with groundwater in Mount Merapi are high utilization compared to other volcanoes worldwide, changes in land use, pollution, and its lowering table. Therefore, this study aims to compare the hydrogeological characteristics and aquifer systems of the southern and southeastern parts of Merapi Volcano. The hydrogeological characteristics were obtained from geological mapping, surface and subsurface, as well as rock XRF tests. Meanwhile, the hydrogeochemical characterization was determined through chemical data using the Trilinear Piper, Kurlov, Fingerprint, Composition, and Harker Diagram methods. The results of the Trilinear Piper, Kurlov, Fingerprint, and Composition Diagram methods show that Mount Merapi has 3, 7, 4, and 2 types of patterns different from other volcanoes in the world. On the other hand, the Harker diagram has the same pattern of Mg-Ca and Mg-Na as several other volcanoes. In conclusion, the hydrostratigraphy in the southern part of the volcano, consists of aquifuge, aquiclude, and aquifer, while in the southeast, there are aquitards of volcanic sandstone and tuff.

Determination of Groundwater Recharge Area by Using Hydroisotope Technic of Sei Bingei Area and Surrounding Areas, Langkat Regency, North Sumatra