Ttukdo Arisu Water Purification Center, the first modern facility of its kind in Korea, commenced operations in September 1908. From then until Korea was liberated from colonial Japanese rule, the water quality was examined in accordance with 14 parameters, such as turbidity, pH, hardness, and dissolved solids. 
On March 11, 1963, the Regulation on Health Diagnosis & Hygiene was passed, setting new standards for water quality. New criteria for inspections and additional parameters were set to include ammonium nitrate and 28 other items.
However, the quality of tap water became the subject of controversy. In August 1989, it was reported by the media that tap water was contaminated with microorganisms and heavy metals. In 1990, trihalomethane and other disinfectant byproducts were found in the tap water. In the following year, phenol leaked from Doosan Plant in Gumi, contaminating the source water for the Nakdong River, where odor was detected in 1992. This succession of reports on contaminated tap water created profound distrust in the general public, who were convinced that all tap water was contaminated and was unfit for drinking. To reverse this distrust, efforts were made to prevent contamination, expand the scope of water quality inspection, and establish a systematic framework for those inspections. From July 1997, Seoul instituted 2 more of its own inspection criteria on top of the statutory parameters. Today, the city has 104 monitoring and 59 statutory inspection parameters. Beginning in 2014, new items are added each year, such as disinfectant byproducts and trace contaminants. Arisu, Seoul’s tap water, is monitored and inspected in accordance with WHO (World Health Organization) guidelines and announced to the public as evidence of its safety.
Seoul instituted an algae alert system in 2000 to respond effectively to an increase of odor-generating algae at the water source. However, there have been cases where odor was detected in the tap water even though the algae alert was not activated. In addition to the algae alert system, Seoul introduced an odor alert system in 2012 to monitor geosmin and 2-MIB to react preemptively and proactively to odor-generating particles in order to keep tap water free of odor and bad taste.
As of 2014, there are 59 parameters in the statutory water quality inspection.

 ① Water source management ⇒ Ensures safety and quality at source (intensive management during dry and other vulnerable seasons).

 ② Purification management ⇒ Maintains the best possible purification quality (turbidity kept below 0.06NTU on annual average).

 ③ Supply-level management ⇒ Provides proactive administrative services (Arisu Quality Certification, etc.).

 ④ Inspection at faucet and supply level ⇒ Improves acceptability and quality of the tap water as felt by residents (inspection at faucet in 450 different locations).

 ⑤ Reduction of chlorine residue at faucet ⇒ Removes odor from tap water (chlorine residue maintained within the range of 0.1 – 0.3mg/L).

Multi-check Quality Inspection System for Tap Water: Management at Water Source, Purification & Supply Process

Source: Internal data, Seoul Metropolitan Government

Water Quality Management at Source & Intake
Of the 6 purification centers in Seoul, Gwangam is the one that takes raw water from the Paldang Reservoir Protected Area (157.3 km²). The rest take their water from Jamsil Reservoir Protected Area (6.45 km²). Inspections are conducted on the main Han River stream and tributaries that affect intake points. Water quality is then forecast to ensure aggressive and proactive response to the source of any contamination and to safeguard the safety of the water.
Major water quality inspections at source and at intake are carried out by Seoul Waterworks Research Institute (WRI) and purification centers. Water measurements for such contaminants as phenol and ammonium nitrate, are done automatically in real time. The intake points at Gangbuk, Amsa, and Pungnap (Yeongdeungpo) operate a bio alert, constantly monitoring for contaminants such as heavy metals and domestic sewage.

<Table 1> Water Quality Inspection at Source & Intake

Water Quality Management at Purification Centers
With an aim of managing the quality of purified water, turbidity is kept at 0.06NTU or lower (flood season: 0.1NTU or lower in turbidity), and the chlorine residue goal of each purification center is ±0.04mg/L. The turbidity of purified water at the processing level aims to achieve 0.3NTU or lower for 95% or more of the monthly measured sample. Goals for tasteless, odorless water are achieved through odor alerts and powdered activated carbon, etc.
Source water is inspected for quality to enable effective management at the purification processing level while ensuring sufficient disinfection concentration and management of filtered water turbidity, with the utmost effort made to produce tap water of the highest quality even in the most undesirable conditions.
Turbidity is one of the most important parameters in tap water inspection. It is managed 24 hours a day at each step of the process from injection of chemicals for purification. Management is adjusted according to season (dry weather, flooding, winter, etc.) to ensure optimal conditions for processing. The quality of tap water is inspected according to 163 parameters (59 drinking water parameters, 104 monitoring parameters), as strict as WHO guidelines. The inspection agency is the WRI, the highest tap water inspection authority in South Korea, and 6 purification centers, classifying the parameters daily, weekly, monthly, quarterly, and yearly. Results are disclosed to the public as evidence of the safety of the tap water.

<Table 2> Water Quality Management at Purification Centers

From Purification Center to Faucet
In the past, chlorine, one of the most influential factors on people drinking straight from the tap, was injected intensively at the purification centers. This resulted in complaints about the odor in the vicinity; there was also the issue of meeting the chlorine residue standards at the faucet. To resolve these issues, injected chlorine was reduced at Gangbuk and Amsa Purification Centers that supply to wider areas and a system introduced to inject it at the distributing points (17 locations) from 2012. The plan is to introduce the system in phases and maintain 0.1~0.3mg/L at the faucet.
The pipes in use are deteriorating and range from cast iron to galvanized steel to non-corrosive materials. They frequently leak and develop rust inside. The long use of uncoated cast iron and steel pipes left the inside of the pipes covered in rust, interrupting flow and reducing chlorine concentration. In April 1994, galvanized steel pipe was no longer permitted for waterworks. The City of Seoul plans to replace all pipes with a corrosion-resistant network by 2018.
Rooftop water tanks at apartments are a byproduct of the time-restricted water supply system of the past due to poor infrastructure. Because tap water was supplied only at certain hours, most of the water for domestic use was pumped, not directly, but from the underground tank to the rooftop tank. The water would stay in the tank for a prolonged period of time, resulting in the loss of chlorine residue. This could lead to degradation of water quality, including unhygienic storage. The city decided to take the direct supply approach without going through the water tanks. This increased the amount of chlorine residue (0.18mg/L) at the faucet, enhancing the quality and safety of the tap water.

Water Quality Management at Distribution/Supply Level
Several inspection and management methods are adopted at distribution level to ensure that the quality and safety of the water produced at the purification centers is maintained when it is delivered to users. These include statutory inspections, inspections at each distribution and supply process, Arisu Quality Certification, and other such tests that involve resident participation. The city takes various measures to enhance satisfaction and reliability, and to encourage more to drink the tap water.

<Table 3> Water Quality Management at Distribution/Supply Level

Multi-check Quality Inspection for Major Particles: Trace Particles & Algae Alert System
Trace Particles
In addition to the 163 parameters, Seoul set 130 parameters for other items (6 more added in 2014), mostly comprised of endocrine disruptors, unregulated chemicals, agricultural pesticide, and carcinogenic substances, to identify any new trace particles in the annual inspection.

Seoul’s water quality inspection and management is a systematic process that covers start to finish, from water source to production to supply at the faucet. The city delivers tap water that is safe and healthy, and complies with WHO guidelines with the 163 parameters in water quality inspections as well as with the 130 parameters concerned with unregulated trace particles in the annual inspection. The city is aware that odor is the biggest reason people avoid drinking from the tap and has therefore adopted the algae and odor alerts that are activated upon detecting odor-generating substances or algae at the water source. This preemptive action has helped the city detect and remove odor-generating substances. To reduce chlorine and disinfectant odor, Seoul injects chlorine at the distribution reservoir, limiting the chlorine within the guideline range of 0.1 – 0.3mg/L. When more advanced water purification facilities are completed and adopted by all 6 purification centers in Seoul by 2015, the city will be able to drastically reduce odor and taste-generating substances in the tap water

Seoul endeavors to maintain the safety of the raw water at its source at Paldang Reservoir and constantly monitors for contaminants at intake points. Raw water is analyzed by the purification centers in accordance with various parameters as stringent as WHO guidelines. Seoul’s odor alert, the first in South Korea to respond proactively to increases in algae, as well as the at-faucet inspection called the Arisu Quality Certification, distributed chlorine injection, and monitoring and analysis of trace particles are all part of the multi-check approach adopted by the city to supply safe, healthy tap water to its residents. Each year, research topics are selected and studied by each purification center, and the outcome presented in workshops where the issues and improvements are examined for other cities and developing countries to refer to.

- Why take a multi-check approach in producing tap water?
Paldang Reservoir, Seoul’s water source, is not algae- or contaminant-free, making it necessary to conduct statutory inspections and monitor water quality across the whole process, from source and intake points to purification centers and distribution and supply points, so as to ensure safety of the tap water supplied to some 10 million people.
 
- How were the quality standards developed for Arisu?
In South Korea, the drinking water standards govern the amount of microbes, harmful inorganic and organic substances, disinfectants and disinfectant byproducts, and substances for aesthetic considerations. The parameters are usually determined by the amount that would not be detrimental to health for an ordinary person drinking 2L of water daily for 70 years, with the additional consideration of a safety factor of 1/100 – 1/1,000. This means that drinking water that meets the standards will not be detrimental to human health.
 
- How are the water quality monitoring parameters selected and what is their basis?
Pursuant to Article 26.3 of the Water Supply & Waterworks Installation Act, tap water quality inspections are reinforced by selecting specific parameters on such contaminants as: i) trace particles that are harmful and are highly likely to be detected in the annual inspection or the city’s inspections; ii) those that have become the subject of social controversy and need to be tested; and iii) those that have caused problems in the international community and may be found in South Korea as well. The inspection standards, methods, etc. are in compliance with WHO regulations and examples from other countries (30 parameters selected by the Ministry of Environment and 104 parameters by the City of Seoul (including the monitoring parameters from the Ministry of Environment)).
 
- How were the Healthy, Taste-Free Water Guidelines developed?
Since May 2010, various activities have been undertaken such as studies by research institutes, tasting events, public polls, public hearings, and expert advisory meetings, etc. The Guidelines were developed and completed in December 2010.
 
<Table 6> Healthy, Taste-Free Water Guidelines

The Office of Waterworks, Seoul Metropolitan Government, http://arisu.seoul.go.kr/
The Office of Waterworks, Seoul Metropolitan Government, 2013, Report on Tap Water Quality.
Ministry of Environment, 2008, The 100-Year History of Waterworks in Korea.