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Not many people realize that human life has been sustained by only 0.5% of freshwater on Earth. A very small part of this freshwater is hidden – unseen water that is stored deep under the earth in limestone, or karst aquifers. These water sources are now at serious risk due to mining activities, and local communities are trying to find creative ways to access and maintain their freshwater supply.
The World Health Organization (WHO) has stated that 25% of human freshwater needs on earth come from water stored in limestone or karst aquifers (Ford and William, 2007). Different from water in other types of rock aquifers, water in karst aquifers is difficult to predict from the ground surface even with the help of the most advanced geophysical survey equipment. This karst water flows through cave passages, tens of meters to hundreds of meters underground. Karst water forms rivers, waterfalls, lakes, fountains, or droplets from the tip of the stalactites in the darkness of the cave. It has extraordinary power, as it can carve limestone into caves with various shapes, and create various beautiful and eccentric forms of cave sediment.
Karst water is the foundation of life for people who live in limestone areas, where limestone areas are visually dry areas. Some of this karst water naturally comes out into springs, but much of it must be pumped so it can be used by the surrounding communities. Unfortunately, karst water is very vulnerable to disappearance. Excessive exploitation of limestone, alongside disregard for the precautionary principle (Langer, 2001) will eliminate the function of limestone as a valuable freshwater aquifer.
Industry demand for limestone disrupting natural flow
As a rare mineral, limestone is also the main material needed for industrial extraction. In an era where many countries are competing to build mega-cities, limestone is being turned into the main material for roads, buildings, dams, airports, and more. Water reserves are being destroyed in limestone areas and are in danger of being lost.
Due to its natural properties, mainly the presence of cracks, limestone quickly absorbs water. But to store water, limestone must also have many cracks and crevices filled by soil. Limestone areas have thick soil cover only if the surface is covered by vegetation, for example, forest.
The limestone part that stores the most rainwater is near the ground surface, also known as the epikarst layer. Epikarst has a thickness of not more than 15 meters and is located at a depth between 10 cm–30 meters from the surface. The sustainability of underground river water in karst areas is highly dependent on the conditions of the epikarst. Under undisturbed epikarst conditions, the underground river water will continue to flow for thousands of years.
In addition to deforestation, limestone mining activities are a massive disturbance to the epikarst. Due to its proximity to the surface, the most significant disturbance to epikarst is the changing landscape by human activities. However, legal and illegal mining is still ongoing in several locations, with some located in underground river catchment areas where the water is for community use.
The case of Gunungkidul Regency
Gunungkidul Regency is the largest district in the Special Region of Yogyakarta, Indonesia, with a population of approximately 770,000 people (Central Statistics Agency, 2019). Around 51% of this district is a karst area formed by limestone, naturally hard but easy to crack. Because the epikarst is prone to disturbance, the government has protected most of the karst area in Gunungkidul Regency.
German researcher Franz Wilhelm Junghuhn, who came to Java in 1835, had noted that in 1850 most of the limestone areas in Gunungkidul were still covered with dense forests, especially those near the coastline. Meanwhile, close to residential areas, the limestone hills have more or less turned into agricultural land. Researchers believe that massive deforestation has changed the face of the limestone area of Gunungkidul today (Sunkar, 2008)
As a result of the loss of forests, natural springs and lakes are currently only seasonal. Water is easy to find during the rainy season, but it disappears quickly when the dry season comes. Gunungkidul Regency has a different season pattern compared to the surrounding areas: the rainy season is only for 4–5 months, while the dry season is more extended for about 7–8 months. This situation causes hundreds of thousands of residents of Gunungkidul to face a freshwater crisis every year.
The karst area in Gunungkidul, which now looks drier, was once overgrown with dense forest, as Junghuhn had reported in 1850. The forest has now disappeared, but there are remnants of the ancient forest that still exist today. Limestone mining activities in Gunungkidul are still operating today. Many of them are located in the underground river's water catchment areas. For example, some limestone quarries are located in the Seropan Cave and Bribin Cave underground river's water catchment areas.
Based on expert research, this mining has a negative impact on the character of underground river flows and water quality. Due to limestone mining, the water discharge decreases in the dry season due to the loss of the main water storage layer in the limestone (epikarst). In contrast, in the rainy season, the water discharge increases drastically beyond the capacity of the cave passages, causing flash floods in the cave. Stripping the surface layer of limestone also allows contaminants from the surface to enter underground streams quickly.
Even though the karst surface in Gunungkidul currently looks dry, several rivers flow in the caves. This river’s water comes from the accumulation of rainwater stored in limestone. Several large underground rivers have been used to fulfill the population's freshwater needs. For example, the underground river in Bribin Cave has been pumped and operated since 1985. However, the operational costs are quite expensive because the pumps use electricity from the state grid.
In 2000, the Indonesian government, in collaboration with the Federal Ministry of Education and Research in Germany (through the Karlsruhe Institute of Technology), optimized Bribin Cave underground water by adding a water pumping point that utilizes water pressure energy from a dammed underground river. Running since 2010, this collaborative project installation can supply water to 82,000 people.
Besides the Bribin Cave river, underground water has also been used from other caves, such as Seropan Cave and Ngobaran Cave, which still rely on the state electricity grid for pumps. But the hilly natural conditions, the large area that must be served, and a large number of residents mean that not everyone living in limestone areas are covered by freshwater services.
Until this time, every dry season, many poor people in Gunungkidul Regency still take leftover water from dry lakes. Some of them are still carrying water from the cave manually. They often have to bathe or wash clothes in the lake with their livestock. This condition shows how they have survived the freshwater crisis because not all families can buy water every month in the dry season. The harsh natural conditions and difficult life place Gunungkidul as a regency with a high suicide rate in Indonesia.
Pumping water from Pulejajar Cave to fulfill Jepitu villagers' freshwater needs
In 2021 the number of people facing a freshwater crisis reached close to 130,000, spread over 12 subdistricts. Jepitu village (in Girisubo sub-district) is 24 kilometers from Bribin Cave, however the hilly natural conditions make the freshwater from Bribin Cave unable to maximally service the residents of Jepitu and the surrounding villages. Water does not flow regularly, and not all residents have access to the water distribution network managed by the Gunungkidul Regency water authority. Residents use rainwater to fulfill their needs in the dry season or buy water for 100,000–150,000 Indonesian rupiah per tank (5,000 liters). The short rainy season often needs more than the rainwater supply to last through the dry season.
A group of students discovered an underground river flow in a cave in Jepitu Village in 2008. The cave was named Pulejajar, and on the second day of cave exploration, three villagers, Mr Rubiyanto, Mr Paryo, and Mr Sulis, joined the students to map the cave. At that time, Rubiyanto had an idea to pump water from Pulejajar Cave to fulfill the villagers' freshwater needs.
Rubiyanto took advantage of the village fund from the government and also crowdfunded money to start the initial work in Pulejajar Cave. He and the village community then organized dozens of volunteers from various institutions and backgrounds to work together to build a pipe installation in the cave. Success came as water flowed at a rate of 1.23 liters/second with a 2-inch diameter pipe to the cave entrance in 2016. The total length of the pipe installation from the water intake point to the cave entrance is 1.3 kilometers. However, the amount of water that came out at that time still needed to be increased to fulfill the villagers' water needs.
Rubiyanto and his community then raised further funds from the wider community. He managed to get sufficient financial support to optimize the water coming out of the cave. Through cooperation for several years with various communities, two different networks with 3-inch diameter pipes were finally successfully installed in the cave. The underground river water discharge that has successfully flowed to the cave entrance totals 6.7 liters/second.
The location of the settlement of Jepitu Village residents is quite far from the Pulejajar Cave entrance location (5.5 kilometers). The position of the entrance to the cave is also lower in elevation than the position of the residents' settlements, which is 86 meters higher. Following guidelines from YouTube, Rubiyanto uses a hydraulic ram pump that works without electricity by utilizing water pressure to push the water to a higher position. Water from the cave entrance is pumped into a communal reservoir near the settlement to be used by the village community. The local community also operate trucks with 5,000-litre tanks capacity to distribute water to locations that do not have access to freshwater. They supply water from Pulejajar Cave for free to public facilities in the villages, such as schools, mosques, churches, and village government offices. The community also provides the purchase of water at a much lower price than the usual cost.
The method for flowing water from the intake point in the cave to the entrance uses the force of gravity. This method is more effective and cheaper than a pump that requires electric power. Cave water contains high calcium and magnesium minerals, often causing the pump to be unable to work for a long time due to a large amount of sedimentation. Using electricity from the government grid is also quite expensive to operate the pump continuously. The use of electric-based pumps requires intensive maintenance and high operating costs.
As the leader of a village youth organization called Kombi (‘Embracing the Earth Community’), Rubiyanto and his community have been actively protecting their village environment since 2005. Jepitu village has several beaches that have been opened for tourism and are famous in Yogyakarta Special Region, and the community has also been fighting thefts of coral reefs and sea sand, and illegal fishing, in their village.
Since discovering a freshwater source in Pulejajar Cave in Jepitu in 2008, Rubiyanto and his community have focused more on how villagers can access fresh water and no longer depend on government assistance, nor do they have to buy water at a high cost. Rubiyanto has occupied a central role in flowing water in the Pulejajar Cave to the surface. He organized dozens of volunteers from various backgrounds, including villagers, cave exploration groups, soldiers, police officers, students, academics, and researchers.
In search of solutions to the freshwater crisis in Gunungkidul
Limestone caves are an ecosystem that has enormous potential for freshwater. The method of utilizing cave water, as done by Rubiyanto and his community, is the right solution for people who live in an environment composed of limestone. In the case of Gunungkidul Regency, the Gunungkidul Regency water management authority has said that the water needs of the people of Gunungkidul are not enough to rely on large systems such as in Bribin Cave and Seropan Cave. Like what Rubiyanto and his community have done, small communal systems are needed so that people are more independent in fulfilling their daily water needs. In 2020, the Gunungkidul regency government distributed freshwater assistance to as many as 2,200 trucks with 5000-liter tanks in various areas that do not have access to fresh water.
The geological conditions of the limestone areas in Gunungkidul do not allow the search for water through the geophysical survey method. Various geophysical surveys have been carried out since 1975, but the success rate could be much more significant. Community involvement in efforts to find water sources in caves has become one of the most effective ways to find water sources. According to data, in Gunungkidul, 617 caves have been identified. So the possibility of finding flow systems, like the Pulejajar Cave, is still huge.
The utilization of water from underground rivers in karst areas is more environmentally friendly than water from wells. Underground river water in the karst area comes from rainwater stored in limestone bodies. Naturally, this water will come out of the limestone following the law of gravity, accumulate in underground rivers, and flow into the sea throughout the year. Pumping water from the underground river in caves, in principle, only deflects the flow of water so that it can be used before it is dumped into the sea. So that does not affect the stability of groundwater.
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A.B. Rodhial Falah is researcher on Speleology (study and exploration of caves) and filmmaker. He has written articles and publication on speleology and karst ecosystem and has produced news documentary on the topic of Environment, Energy, Pollution and Climate Change in Indonesia, mostly for the Global Ideas series for Deutsche Welle. He holds Bachelor of Geology Engineering from National Institute of Technology, Yogyakarta.
The views expressed in this article are not necessarily those of Heinrich Böll Stiftung.