By research, hydrogeologists found that volcanic mountain springs fulfill the three conditions of groundwater quality characteristics, namely quality, quantity, and continuity. Quantity is influenced by rainfall, water cycle and hydrogeological conditions of the area around the water resources. Quality is influenced by natural factors (conditions and composition of soil and rocks) as well as human activities (agriculture, household pollution, industry, etc.). While continuity gives a balance between usage and recharging.
Groundwater starts from a hydrological cycle, where clouds are composed of millions of tiny drops of water, so light that these droplets can float in the air, then lifted up by the warm air flow from the ground and eventually turn into rainwater that falls to the earth. The water permeates and is deposited beneath the soil surface, which is then due to the effect of gravitational forces moving vertically through the soil layer until it reaches the water saturated zone and is finally deposited in a layer of water-carrying rock called an aquifer.
Based on the constituent material and its physical environment, there are several types of aquifers, namely allifial fan aquifers (located in coastal areas, sedimentary and surrounding areas), sedimentary aquifers (peat, organic), karstic aquifers (limestone mountains) and volcanic aquifers volcanoes), which is the best source of fresh water. Aquifers are layers or rock formations capable of storing and passing water in significant quantities, capable of providing supplies to wells or springs. Indonesia is a wet tropical region with relatively high rainfall and geologically located in the volcanic arc area. Indonesia has more than a hundred active and inactive volcanoes. Geologically the volcanoes form rock layers that are very conducive to acting as aquifers.
During the drainage, groundwater undergoes various processes that make the groundwater contain a variety of minerals and ultimately have different qualities in each place. As a continuation of natural processes, groundwater then appears on the surface and is called a spring. In this case, the springs in the mountains are regarded as the perfect source of water, both quantity and quality. Mountain springs in the mountains are generally large and continuous because in this area is generally a wet area with high rainfall intensity and still has a relatively good catchment area.Cyclus of water in nature (Source: http://kimlingiwill.blogspot.com/2010/11/pegunungan-vulkanik-sumber-mata-air.)