Where does Seoul's drinking water come from?

Ttukdo Arisu Water Purification Center in Seoul / Courtesy of Seoul Metropolitan Government

6 treatment plants process 3.17 million tons of water every day

By Kim Se-jeong

A recent tap water crisis in Incheon has attracted public attention about the quality of drinking water in cities across the country. Larvae were found in tap water across Incheon, Busan and parts of Gyeonggi Province, raising questions among the public about where their water comes from and how it is processed.

In Seoul with nearly 10 million residents, tap water comes from the Han River. The Seoul Metropolitan Government runs six water treatment plants in and near the city which together process 3.17 million tons of water every day and also takes care of the network of pipes that deliver the water.

Water is collected from eight spots upstream where quality is best. Arriving at a treatment plant, chemicals are added to the water to neutralize the dirt and other contaminants. The chemical reaction results in the formation of aggregate called floc.

The next phase of treatment is sedimentation where the heavier floc settles to the bottom of the water. Meanwhile, the clear water on top passes through filters of sand, gravel and granular activated carbon. Ozone is also added as part of the disinfection process. Filtering water through carbon and adding ozone are not always part of the water treatment process, globally speaking, but Seoul city, along with other major cities in Korea, have added those steps to ensure water quality.

Disinfection is the final phase in which chlorine or chloramine is added to kill remaining bacteria, viruses and parasites. Chlorine also protects the water from germs that can exist in the pipes.

The processed water is piped to about 100 storage facilities across Seoul before being sent to homes and businesses.

The entire process occurs under a roof and the facility is well-contained to protect water from insects, leaves and general airborne matter. The treatment plant staff are also required to wear protective suits when entering the facility, in an effort to prevent contamination.

"We can guarantee that residents don't have to worry about the safety of their drinking water in Seoul," said an official from the city government's waterworks authority.

292 liters of water per person

One Seoul resident uses an average of 292 liters of water per day, according to city statistics. That is more than Londoners who use 181 liters on average but less than New Yorkers who use 454 liters.

The price of water in Seoul is cheap, compared to other cities in the world. Seoul charges an average of 566 won per cubic meter of water (or 1 ton), four times cheaper than London and 5.9 times lower than New York City. For individual homes, Seoul charges 402.9 won per cubic meter, while for businesses it charges 987 won with the exception of those who run public sauna businesses who pay only 477 won.

The city is in the process of increasing water bill fees. City council is reviewing the new water rate increase proposal. If adopted, the new rates will go into effect from Jan. 1 next year.

But which entity consumes the biggest amount of water in Seoul?

In 2019, Seoul National University consumed the most, followed by COEX and Lotte World, according to the city government.

Leakage is always a headache for the city water supplier and the city government has been dedicated to replacing old pipes. Between 2016 and 2019, it replaced about 13,400 kilometers of pipes, accounting for 99.5 percent of the entire pipes running under the city's surface. If water pipes in your home are too old, the city government will provide a subsidy for replacement. The leakage rate is less than 5 percent.

Toilets are another major area for leakage. The city estimated almost 7.04 million tons of water was wasted from Seoul toilets between 2016 and 2019.

History of drinking water treatment

Seoul's first water treatment plant opened in 1908 on today's Ttukseom near Seoul Forest. The building is currently serving as a museum. Courtesy of Seoul Metropolitan Government

Seoul's first drinking water treatment plant opened in 1908 when the city had approximately 200,000 residents.

Before then, people drank water from wells or directly from the river or streams.

Wealthy people had their own wells on their properties. The poor had to travel to the nearest well or stream to collect water. On Sept 2, 1897, Tongnip Sinmun, the local newspaper, reported one resident in Seoul had access to less than five bowls of water, equivalent to 10 liters a day. To put that in perspective flushing a modern toilet uses more than 10 liters of water.

Those who could afford it also paid people to deliver water to their home. According to "Easy Seoul History: During Japanese Colonization," a book published by the Seoul Histography Institute, Seoul had about 2,000 water businessmen at that time.

The first drinking water treatment plant was built by American Korean Electric Co., a private U.S. company. They built the plant at Ttukseom near present-day Seoul Forest.

The plant took water from the Han River and filtered it. The clean water was piped to a storage facility, located in today's Geumho-dong, before being sent to four sections of the city. The book said it served around 120,000 residents in Seoul, mostly Japanese and other foreign residents in the city. Many locals couldn't afford to have tap water in their homes, so they would share a single tap with neighbors.

Workers install a pipe to collect water from Han River in this undated photo. Courtesy of Seoul Metropolitan Government