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

<Figure 1> Water Quality Inspection 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 the 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 water.

Major water quality inspections at source and at intake are carried out by Seoul’s 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 system, 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), 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 disinfectant 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, and 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 tap water safety.

<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 faucet. To resolve these issues, injected chlorine was reduced at Gangbuk and Amsa Purification Centers, which 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 has 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.

<Figure 2> Reducing Disinfectant Odor(Chlorine)

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

Algae Alert System

To reduce the source of odor in tap water, an algae alert system is activated when blue-green algae is identified at the water source, after which the water can be treated accordingly. In 2012, the algae alert was activated for a total of 15 days at Upstream Point 1 of Jamsil Reservoir. From 2000 to date, 6 algae warnings have been issued at Han River segments in Seoul. The effects of green algae include odor, water toxicity, and damage to water purification devices, etc. Along with the algae alert system at Jamsil, Seoul introduced an odor alert system for odor-generating substances – geosmin and 2-MIB – in 2012. The city has been able to respond proactively to such substances, thereby effectively reducing odor before the water reaches the tap. When an alert is issued due to significant amounts of algae and odor-generating substances, water inspections increase in frequency from weekly to daily, accompanied by various purification measures (injecting powdered activated carbon, stopping the injection of chlorine before the intake points and injecting it after PAC treatment at the purification centers), in order to minimize odor before the tap water goes into the supply pipes.

Supply of Healthy, Safe Water

Seoul endeavors to maintain safety of 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 at-faucet inspections known as 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 to which other cities and developing countries can refer.

- Why take a multi-check approach to 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 allowed, as well as other 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 highly likely to be detected in annual inspections 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 ).

- 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.