Sistema de Inspección de la Calidad del Agua del Grifo a través de Múltiples Pruebas

Date 2017-05-03 Category Agua potable Updater ssunha
Yong-Mo Cho
the Seoul Institute
Last Update


①   Water quality management of the water supply source ⇒ Securing safe water quality of raw source water (Intensified management during vulnerable periods like periods of water shortage)
②   Purified water quality management ⇒ Maintenance of optimal purified water quality (Turbidity: less than 0.06 NTU in annual average)
③   Water quality management during the process of water distribution and supply ⇒ Establishment of outreach administrative services (Arisu quality confirmation system, etc.)
④   Water quality inspection at the faucets and supply process ⇒ Improvement of water quality experienced by the citizens (Inspection of faucets at 450 places, etc.)
⑤ Reduction of residual chlorine of the faucets ⇒ Supply of good tasting and odorless tap water (Residual chlorine: maintained at the level of 0.1~0.3mg/L)



Since the Ttukdo Arisu Purification Center, the first modern water purification plant in Korea, started to generate tap water in September 1908, water quality inspection had been evaluated for 14 items including turbidity, pH, hardness, residue on evaporation, etc. until Korea was liberated from Japanese colonial rule in 1945. When the “Regulation on the Medical Examination and Sanitation” was enacted on March 11th, 1963, standards of water quality and selection of water quality inspection items were determined, and the number of legal water quality inspection items increased to 29 items including ammonia nitrogen, etc.
It was reported in the press that the tap water was contaminated with microorganisms and heavy metal in August 1989. Disinfection by-products such as trihalomathane were detected in the tap water in 1990. Nakdong River, one of the sources of tap water, was polluted because of illegal disposal of phenol by the Doosan in Gumi in 1991. Filthy odors originating from Nakdong River were reported in 1992. As these incidents kept occurring over the years, the quality of tap water emerged as one of the main social issues. The consecutive incidents of tap water contamination inevitably resulted in the distrust of tap water, and accordingly tap water was recognized by the people as contaminated water that was not suitable for drinking.
In order to overcome this distrust, the Seoul Metropolitan Government put forth efforts to prepare for contamination incidents and to establish the water quality inspection system by expanding the number of water quality inspection items and strengthening the inspection itself. Seoul selected 2 more items to be included for water quality monitoring in addition to the established legal items for water quality inspection in July 1997. Since then, Seoul has expanded the items continuously and now performs water quality monitoring for 104 items, and water quality inspection for 59 legal items. In 2014, Seoul added trace amounts of toxic substances such as disinfection by-products to the inspection item list year by year. Finally, Seoul began carrying out water quality inspections that included all items designated by WHO (World Health Organization), and announced the inspection results to the public so that Arisu, the tap water of Seoul, could be proven to be safe tap water.
To effectively cope with the problem of filthy odors generated largely due to the increasing algae around the catchment areas, Seoul has operated the algae warning system since 2000. However, the incidents of bad smelling tap water occurred even when algae warnings were not issued. Seoul started to operate a smell warning system for the geosmin and 2-MIB items for the first time in Korea in 2012 in addition to the algae warning system to respond to and treat the odorous substances preemptively and efficiently in order to supply good tasting tap water without the smell.
As of 2014, Seoul performed water quality inspection for 59 legal items.


Main Contents of Tap Water Quality Management

Water Quality Management System using the Multiple Test Methods: Water Quality Management by Raw Source Water, Purified Water and Water Supply System

<Figure 1> Water Quality Inspection System by Raw Source Water, Purified Water and Water Supply System


Water Quality Management of Water Supply Sources and Intake Raw Water

Of the 6 water purification plants in Seoul, Gwangam purification center obtains its raw water from the Paldang water source protection area (157.3㎢) and 5 water purification plants, including Gangbuk purification center, obtain their raw water from the Jamsil water source protection area (6.45㎢). Seoul makes efforts to ensure safe raw water quality by forecasting the water quality and handling pollution sources actively via water quality inspection of the main stream of Hangang and its tributaries, which influence water supply sources.   
The main water quality inspections of water supply sources and intake raw water are conducted by the Water Supply Institute and the purification centers. 7 items including phenol, ammonia nitrogen, etc. are inspected using an automatic water quality measuring system in real time. Biological warning systems are operated in the Gangbuk, Amsa and Pungnap (Yeongdeungpo) purification centers to monitor the inflow of pollution sources such as heavy metal and domestic sewage constantly via multiple tests.
<Table 1> Status of Water Quality Inspection for Water Supply Sources and Intake Raw Water
Classification Inspection
Inspection Items
Water Supply Source 20 Places (South Hangang 5, North Hangang 5, Kyeongancheon <Stream>, Tributaries on the Paldang Downstream 9) 42 Items Water Supply Institute Monthly 17
Quarterly 25
Water Supply Source 8 Places: Tributaries (6), Main Stream of Hangang (2)
- Tributaries: Gungchoncheon, Dosimcheon, Wolmuncheon, Deoksocheon, Hongneungcheon, Sangokcheon (Stream)
- Main Stream of Hangang: Amsa, Guui
57 Items
- Tributaries: 42 Items
- Main Stream of Hangang: 15 Items
(15 Items Overlapped)
Water Supply Institute Monthly 42
Amsa, Guui Daily 4
Monthly 11
Water Intake Source 3 Places
- Gangbuk: Green Algae, Closterium (Heavy Metal, Agricultural Pesticides)
- Amsa: Electric Active Microbes (Domestic Sewage)
- Pungnap: Water Flea (Insecticide, Heavy Metal)
Biological Warning System Gangbuk, Amsa, Yeongdeungpo Real Time
Water Intake Source 6 Water Intake Stations: Cyan, Phenol, NH3-N, TOC, Water Temperature, pH, Turbidity (Chlorophyll-a) Automatic Water Quality Monitoring System
(7 Items)
Water Purification Center Real Time
Water Intake Source 10 Places (Water Intake Stations 6, Hangang Confluence 4)
- South Hangang: Bogpo-ri, Sinwon-ri
- North Hangang: Sambong-ri, Jinjung-ri
142 Items
- Legal: 31
- Self: 111
(15 Items Overlapped)
Water Supply Institute 135 Weekly 21
Monthly 12
Quarterly 73
Yearly 29
Water Purification Center 22 Daily 10
Weekly 12
Source: Internal Data of the Seoul Metropolitan Government.

Water Quality Management of Water Purification Centers

The goals of purified water quality management are to maintain Turbidity levels of 0.06NTU and less (Purified water turbidity 0.1NTU and less in the rainy season) and to maintain a ±0.04mg/L level of residual chlorine by purification center. The goal regarding the water purification standard is 0.3NTU of turbidity and less in 95% of the purified water measured every month. The goal in terms of water taste and smell is to produce tasteless and odorless water (by operation of odor warning system, input of powdered activated carbon, etc.).
To manage the water quality in the purification process, Seoul analyzes the water quality of raw water, secures enough disinfectant concentration and manages the turbidity of purified water. Seoul produces and supplies high quality tap water which meets the purification processing standards even in the worst conditions.
In order to manage the turbidity of purified water, which is one of the most important aspects of water quality, Seoul’s system automatically monitors the turbidity during each treatment process from the point of injection of disinfectant for 24 hours. Also, it analyzes and determines the optimal operating conditions for purification processing by season (periods of water shortage, rainy season and winter season). Tap water quality inspections are performed by the Water Supply Institute, the best inspection agency in Korea, and 6 water purification centers in accordance with the WHO (World Health Organization) level of 163 inspection items (59 items for quality of drinking water and 104 monitoring items of Seoul). The items are classified into daily, weekly, monthly, quarterly and yearly ones for water quality analysis, and the inspection results are open to the public to prove the safety of the tap water.
<Table 2> Water Quality Inspection Status of Water Purification Centers
Classification Inspection
No. of Inspection Items
in Total
Raw Water 6 Water Purification Centers 22 Items Water Purification Center Daily 10
Weekly 12
Purified Water 6 Water Purification Centers 23 Items Water Purification Center Daily 10
Monthly 13
Purified Water 6 Water Purification Centers
10 Places (Including 1 Bottle Water)
163 Items
(Legal - 59,
Water Supply Institute Monthly 63 (Legal-59, Monitoring-4)
Quarterly 61
Yearly 39
Purified Water Research on the Real State of New Micro-pollutant
- Residual Pharmaceutical Compounds (3), Industrial Chemical Materials (3)
130 Items
(2014: 6 Items)
Water Supply Institute Yearly
Source: Internal Data of the Seoul Metropolitan Government.

From the Water Purification Center to the Faucet

Chlorine levels have the most influence on whether or not people drink water directly from the tap. Previously, the chlorine was added mainly at the water purification centers. As a result, civil complaints about the chlorine smell were raised by people near the purification centers and the content of residual chlorine was below the standard compared to the faucets far away from the centers. To solve these problems, in 2012 Seoul reduced the amount of chlorine added at the Gangbuk and Amsa purification centers, which provide the largest areas with tap water, and began adding chlorine at places like water distributing reservoirs (17 places) during water transportation. It planned to the system more to the other places to maintain a chlorine level within 0.1~0.3mg/L.
The time-worn water supply pipes made of gray cast iron, galvanized steel and non-corrosion resistant steel were vulnerable to water leaks and rusting inside them. Especially in the case of the cast iron pipes and steel pipes without cladding, the inside of the pipes became covered with rust after a long time of use and accordingly, caused to lower the water flow rate and to reduce the concentration of residual chlorine. The use of galvanized steel pipes for water supply was prohibited in April 1994. Seoul is planning to change the entire pipe system with corrosion-resistant pipes by 2018.
Water tanks on apartment rooftops were installed in the past because of restricted water supply. Due to the insufficient infrastructure, the water supply had been available for a limited time only. In most cases, the water for personal use was supplied after pulling up the from the underground water tank to the rooftop water tank to store it for a necessary period. Because the water was stored for a long time in the water tanks, the loss of residual chlorine occurred, and the water quality could be deteriorated because of the polluted tanks. To address these problems, Seoul started directly supplying water to the households to increase the amount of residual chlorine (0.18mg/L) and to ensure cleanliness and safe water quality.
<Figure 2> Reduction of Disinfectant Smell (Chlorine)


Water Quality Management of Water Distribution and Supply System

To keep the water named Arisu that was produced in the water purification centers clean and safe until it arrives to the household using thorough water quality inspection and management of the water distribution and supply system, Seoul operates and performs several programs and inspections; legal water quality inspections, water quality inspections during each stage of the water supply process, the Arisu quality confirmation system which included participation from citizens, enhancing user confidence and satisfaction to raise the rate that people drank water directly from the tap with the Arisu system.
<Table 3> Water Quality Inspection Status of Water Distribution and Supply System
Classification Inspection Target No. of Inspection Items in Total Inspection Agency Inspection Cycle
Faucets 450 Places (Legal 419 + Basic Inspection Places) 6 Items (Guidelines 4, Self 2) Water Supply Institute Monthly
Old Water Pipes 20 Places 13 Items Water Supply Institute Monthly
During Water Supply Stage 120 Places (Purification Center 8, Before Reservoir 26, After Reservoir 26, Inflow to Water Supply Area 26, Booster Station 8, End of Pipe 26) 11 Items Water Supply Institute Quarterly
Arisu Quality Confirmation System 300,000 Households 12 Items (Primary 5, Secondary 7) Water Supply Office Frequently
Booster Station of Reservoir 113 Places (Reservoir 104, Manned Booster Station 9) Residual chlorine Water Supply Office Daily
Auto Measurement of Water Quality at 188 Places Turbidity, pH, Residual Chlorine, Water Temperature, Electrical Conductivity Water Supply Office Real Time
(Open via SWN)
Distributing Reservoir 104 Places 12 Items Water Supply Office Quarterly
Water Pipe (After Construction) Reservoir, Booster Station, Water Pipe 4 Items (Plumbing 2) Water Supply Office Frequently
Water Pipe and Water Tank Water Pipe 1,079 Places 7 Items Water Supply Office Yearly
Water Tank 12,089 Places 6 Items Private Drinking
Water Quality Inspection Agency
Arisu Drinking Fountain 2,674 Places (30,807 Units) 5 Items Water Supply Office Monthly: Subways
Quarterly: Schools, Public Offices
Monitoring Items Faucets at 25 Places (1 per District) 163 Items
(Legal-59 + Monitoring-104)
Water Supply Institute Yearly
Residual Chlorine
Watershed-based Faucets of Water Purification Center at 90 Places (in 2013) Residual chlorine Water Supply Office Weekly
Source : Internal Data of the Seoul Metropolitan Government.

Water Quality Management Using Multiple Checks for Main Materials: Micro-pollutant and Algae Warning System



Seoul selected 130 inspection items (6 items added in 2014) in addition to the original 163 items and performed research on the actual conditions of the endocrine disruptors like non-regulatory chemicals, pesticides, cancer-causing toxic substances, etc. every year.


Algae Warning System

To reduce the occurrence of substances causing odors in the tap water, Seoul operates the algae warning system, which issues warnings for efficient water purification process when the blue-green algae are present in large amounts in the raw water. The algae warning was issued in section 1 of the upper region of Jamsil underwater dam for 15 days in 2012. 6 algae warnings were issued in the Seoul area of Hangang since 2000. The damages caused by algae include generation of filthy odor and toxic substances, malfunction of water purification facilities, etc. Together with the algae warning system, Seoul started to operate a smell warning system for the geosmin and 2-MIB items in 2012 in order to respond to the presence of odorous substances preemptively to reduce the smell of tap water. In cases when warnings are issued due to the generation of algae and odorous substances in large amounts, the water quality inspections which would normally be performed once a week are carried out one or more times a day, and the input of powder activated carbon and interchlorination after injecting the activated carbon at the purification centers with prechlorination of water intake station stopped are performed to supply the tap water after removing as much of the odorous substances as possible.
<Table 4> Standard of Algae Warning System (Issued when exceeding 2 Items consecutively 2 times)
Items of Algae Warning Algae Watch Algae Warning Large Algae Alarm
Chlorophyll-a Concentration (mg/m3) Over 15 Over 25 Over 100
No. of Cells of the Blue-Green Algae (Cell/mL) Over 500 Over 5,000 Over 106
<Table 5> Smell Warning System (Reflecting the Purification Processing Efficiency)
Items of Smell Warning Smell Watch Smell Warning Large Smell Alarm
Geosmin (ng/L) 20 500 1,000
2-MIB (ng/L) 20 50 100

Water Quality Management System using Multiple Checks: Arisu Quality Confirmation System, Selection and Management of Water Quality Monitoring Items, Water Quality Monitoring through Public-Private Partnership, Monitoring


Arisu Quality Confirmation System

Seoul inspects the water quality during every process of tap water generation and supply and carries on the automatic measurement of water quality. The results are made available to the public via the Seoul Water Now System and the Seoul City Home Page to prove the safety of the tap water of Seoul. However, the citizens drinking the water in their own households are skeptical because rust eluted the insides of the old water pipes in buildings. Seoul visits citizens to check the situation and to inspect the water quality according to the Arisu Quality Confirmation System. It investigates the causes and implements a process to improve the conditions and to gain the trust of citizens.


Selection and Management of Water Quality Monitoring Items in the World Best Class (104 Items)

Seoul legislated and revised the related laws and regulations in cooperation with the Ministry of Environment and related government organizations to set up the management system for tap water quality and water purification standards. In addition to the legal water quality inspection items prescribed in the Water Supply and Waterworks Installation Act, Seoul selected 104 items autonomously to monitor the water quality based on its related ordinances while establishing the laws and regulations related to water supply.

Water Quality Monitoring through Public-Private Partnership

According to Article 30 of the Water Supply and Waterworks Installation Act and the ordinances of the Seoul Metropolitan Government, Seoul organized the Seoul Tap Water Evaluation Committee consisting of external city council members, professors and experts in environmental groups. Seoul collects specimens at 10 points within the water transportation route from the water intake source to the faucets of 2 water purification centers and requested an external private inspection agency designated by the Seoul Tap Water Evaluation Committee to inspect the water quality in regard to the 59 legal water quality inspection items. The inspection results were released via the home pages of Seoul City and the Seoul Tap Water Evaluation Committee to build up the citizens’ confidence in the tap water.

Monitoring System in the Main Points

The residual chlorine is checked every day at 113 places including reservoirs and booster stations. The automatic water quality measuring systems are installed at 188 points to monitor 5 items including turbidity and residual chlorine in real time and the results of measurement are open to the public via the Seoul Water Now System (SWN). 



Healthy and Safe Water Supply

Seoul provides its citizens with healthy and safe water through systematic water quality inspection and management of the entire tap water production and distribution processes from the water supply sources to the faucets. It also has proven the safety of tap water by performing water quality inspections which include the 163 items recommended by WHO and annual research on the actual conditions of micro non-regulatory substances totaling 130 additional items. In order to remove the bad smell and the disinfectant odor which were the main obstacles people had to drinking water directly from the tap, Seoul has operated an algae warning system and a smell warning system which are issued when the algae and bad smell increase in the raw water, reacting preemptively to the substances causing the filthy smell. In order to reduce the disinfectant odors of chlorine, Seoul introduced a system that inputs chlorine at the water reservoirs in the middle of water supply process, maintaining the residual chlorine at the faucets in the range of 0.1~0.3mg/L according to the guideline for tasty water. Once the installation of advanced water purification facilities would have been completed at 6 purification plants in Seoul by 2015, the algae related odor would be reduced remarkably.


Implications and Possibility to Be Applied to Developing Countries (Ripple Effects)

Seoul manages the quality of raw water in the Paldang water supply source and performs constant monitoring at the water intake stations to check the inflow of pollutants. According to the recommendation of WHO, Seoul inspects and analyzes the water quality for many items. It also introduced a smell warning system for the first time in Korea in order to preemptively respond to the algae increase. In addition, Seoul operates Arisu quality confirmation system to inspect the tap water quality at the faucet, and the distributed chlorine injection system to reduce the bad smell of tap water, and performs monitoring and research on micro toxic substances. Tap water quality inspection using the multiple check method contributes to the supply of safe and healthy water. Seoul also selects research subjects for each water purification center and holds workshops to present the research results, problems and improvement cases by purification center. Such research results and cases are used as benchmarks for the other cities, provinces and overseas developing countries. 



- Why do you manage the tap water by checking it multiple times?

The Paldang water supply source for water supply to Seoul is not perfectly free from algae and sources of point pollution. In order to supply safe and healthy water to over 10 million Seoul citizens, Seoul performs water quality inspection and monitoring for various items in multiple levels throughout the entire process of tap water production and distribution including water supply sources, water intake stations, water purification centers, distribution and supply systems, etc.

- What are the water quality criteria of Arisu?

The standards of drinking water quality in Korea include microorganisms, inorganic substances with harmful effects, organic substances with harmful effects, disinfectants, disinfection by-products and substances with aesthetic effects. The reference values of water quality are set by the amount of water that is not harmful to health when an average person drinks 2 liters of water per day for 70 years and in consideration of a 1/100~1/1,000 of safety rate. Therefore, the water within the reference drinking water quality values is harmless to humans.

- What are the bases of selection of water quality monitoring items and inspection items?

According to Paragraph 3 of Article 26 of the Water Supply and Waterworks Installation Act, Seoul selected highly detectable items based on the research on the actual condition of micro toxic substances, etc. and self-inspection results, the necessary items to cope with social issues by inspection, and the items that became issues of tap water in overseas countries which seem to be detectable in Korea as water quality monitoring items. The inspection standards and methods are made and implemented taking the related regulation of WHO and foreign cases into account. (30 items recommended by the Ministry of Environment and 104 items determined by Seoul including the monitoring items for the Ministry of Environment)  

- What are the guidelines for healthy and tasty water?

Seoul carried out research and service agreements with specialized organizations, water tasting events, opinion surveys, public hearings, meetings with advisory committees, etc. since May 2010 to set the guidelines for healthy and tasty water. The guidelines were completed in December 2010.
<Table 6> Guidelines for Healthy and Tasty Water
Classification Item Unit Standards of Drinking Water Quality Guideline Background
Items Related to Health Mineral
(Ca, Mg, Na, K)
mg/L - 20~100 ․ Essential element for body
Total Organic Carbons mg/L 5.0
(Monitoring Items of Seoul)
1.0 and less ․ Good for health by removing the disinfection by-products
Turbidity NTU 0.5 0.3 and less ․ Good for health by removing microorganisms (Protozoa, virus, etc.)
Items Related to Taste Residual chlorine mg/L 4.0 0.1~0.3 ․ Smell of Disinfectant
2-MIB ng/L 20
(Monitoring Items of the Ministry of Environment)
8.0 and less ․ Substance causing moldy odor
Geosmin ng/L 20
(Monitoring Items of the Ministry of Environment)
8.0 and less ․ Substance causing soil odor
Copper mg/L 1.0 0.05 and less ․ Substance causing blue water
Steel mg/L 0.3 0.05 and less ․ Substance causing red water and smell of rust
Temperature - 4~15 ․ Feeling of refreshment and good to drink



Water Circulation Policy Division of the Seoul Metropolitan Government, http://arisu.seoul.go.kr/
Water Circulation Policy Division of the Seoul Metropolitan Government, 2013, Report on Tap Water Quality
Ministry of Environment, 2008, 100 Year History of Korean Water Supply 


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