The most commonly cited cause of sinkholes, which occur more than 100 times a year, is leakage from water and sewage pipes. The pipes laid underground are gradually deteriorating, but replacement work is progressing slowly.
The Ministry of Environment, the governing body responsible for water management, and local governments are shifting responsibility to one another. The Ministry of Environment holds the position that "it is the local government's job to replace aging water pipes," while local governments claim, "It is difficult to replace water and sewage pipes in a timely manner due to a lack of budget." Experts noted that fundamental measures are needed, such as "realigning water and sewage fees" and "increasing efficiency."
According to the Ministry of Land, Infrastructure and Transport, 42.01% (876 cases) of the causes of sinkholes that occurred over the past 10 years (2014 to 2023) were due to damage to sewage pipes, while 12.61% (263 cases) were due to damage to water pipes. This indicates that more than half of the causes of sinkhole incidents are related to aging water and sewage pipes.
The situation is similar in Seoul, which has extensive underground developments. According to the '2025 Underground Safety Management Plan' of Seoul, of the 211 sinkholes that occurred from 2015 to 2023, 50.7% (107 cases) were due to the deterioration of sewage systems and 14.2% (30 cases) were due to aging water supply systems. Six or seven out of every 10 sinkholes were caused by problems with water and sewage pipes.
How do aging water and sewage systems cause sinkhole incidents? Generally, old water pipes develop gaps when joints misalign or break. Water flows out through these gaps, washing away surrounding soil, or soil from above enters the water and sewage pipes through the gaps. Once the soil from above enters the pipe and flows away, the space previously occupied by the soil becomes vacant. Under the influence of gravity, the soil above and the road collapse, resulting in a "sinkhole" phenomenon.
◇ 170,000 km of aging water and sewage pipes nationwide... accounting for 40% of the total
How deteriorated are domestic water and sewage pipes? According to the Ministry of Environment, 37.5% (90,183 km) of water pipes nationwide have been buried for over 20 years, and the aging sewage pipes (75,837 km) account for 44% of the total. Typically, the lifespan of plastic pipes is considered to be 20 years, while that of metal pipes is about 30 years. Therefore, 40% of the national water network is due for replacement.
Experts said, "Just because the lifespan has expired, it doesn't necessarily mean that the sewage pipe must be replaced, but the probability of accidents, such as ground subsidence, naturally increases."
Especially in older urban areas, the deterioration of water pipes is severe. According to the Ministry of Environment, more than half of the water pipes in Seoul (68.6%), Busan (60.6%), and Gwangju (56.2%) have been in place for over 21 years. The deterioration of sewage pipes is also serious in major cities that developed early, such as Daegu (74%), Gwangju (67%), and Seoul (66.1%).
It has been reported that aging sewage pipes were buried at the site of a sinkhole incident in the Gangdong District of Seoul, which recently had a sinkhole approximately 20 meters in diameter. The buried sewage pipes were of two sizes: 600 mm and 450 mm. The 600 mm pipe has been buried for 21 years, and the 450 mm pipe has been in place for over 30 years, with its installation year recorded as 'unknown.' This is due to the lack of proper records when the pipes were buried decades ago.
◇ Local governments say, "Budget constraints make government support essential" vs. the Ministry of Environment says, "It is the local government's responsibility"
Despite this situation, conducting thorough inspections of water and sewage systems and replacing aging pipes is not an easy task. Assuming the replacement of 1 km of water and sewage pipes, the cost would reach approximately 800 million to 1 billion won for water pipes and 1.8 billion won for sewage pipes. It is often necessary to control traffic when excavating and repaving roads, and many citizens express discomfort or file complaints when water supply must be interrupted during water works.
Local governments are expressing concerns about budget shortages. The Ministry of Environment is supporting the replacement of aging pipes in local governments with poor financial situations by providing national funds. If municipalities, which are not special or metropolitan cities, replace aging water pipes, 50% of the expense is covered. For replacing aging sewage pipes, 30% is supported for metropolitan cities, while 60% is provided for other cities and counties.
Metropolitan and special cities, which receive less financial support from the central government compared to basic local governments, argue that additional support from the central government is essential. In response, the Ministry of Environment draws a line by stating, "The replacement and inspection of water and sewage systems are originally the responsibility of local governments," adding that "it is difficult to increase the budget further."
Under current law, the management of water and sewage systems is the responsibility of local governments and water service providers. According to the Special Act on Underground Safety Management, each municipality must inspect underground facilities such as water pipes at least once a year. However, if there is no risk of ground subsidence, inspections can be skipped, leading municipalities to conduct only occasional inspections. The Water Act also imposes regulations for technological diagnosis on local governments.
Some analysts suggest that the replacement of water and sewage systems does not receive strong support from residents, causing it to be deprioritized within local governments.
Kim Du-il, a professor of civil engineering at Dankook University, said, "Because water and sewage pipes are underground, they may go unnoticed even if replaced, and people do not realize their importance until an accident occurs. As a result, local governments tend to neglect them, leading to a decrease in available budgets and frequent neglect."
◇ Producing 1L of water costs 1.07 won, while the selling price is 0.8 won... No funds to repair aging pipes
Experts suggest that to address the budget shortfall, it is necessary to find ways to normalize water rates and increase efficiency.
Currently, local governments are covering the cost of replacing water pipes such as water supply pipes based on 'water fees.' The problem is that the selling price is lower than the cost of producing water, making it practically impossible to generate funds for pipe replacement using revenue from water sales.
According to the Ministry of Environment, the cost of producing 1L of water is 1.069 won, while the average selling price is only 0.796 won. This results in a loss of 0.273 won for every liter sold. The national fee normalization rate (compared to the cost of producing tap water) stands at only 74.5%.
Regionally, Seoul (92.7%), Ulsan (90.2%), and Daejeon (86.8%) are relatively high, but provinces such as Gangwon (52%), Gyeongsangbuk (54.5%), and Jeollanam (56.7%) are selling water at half the production cost.
Ryu Jaena, a research fellow at the Korea Environment Institute (KEI), stated, "There is no ability to repair water and sewage pipes because the cost of producing water is not guaranteed, and local governments will be able to replace aging water and sewage pipes only if they raise water rates."
Professor Kim Du-il also said, "Because there is an attempt to avoid raising public fees, there is no budget to replace aging water and sewage pipes, leading to neglected facilities and ultimately resulting in accidents. Local governments should seek practical solutions, such as raising water fees, instead of relying on the government."