Water Distribution : Shifting to the Direct Water Supply System

Date 2015-06-25 Category Water Supply (Arisu) Updater scaadmin
Seoul Metropolitan Government
Last Update


Ensuring the highest water quality by removing rooftop water tanks and applying the direct water supply system for buildings up to 5 stories high
In 1997, with the goal of removing rooftop water tanks of small buildings – which served as a loophole in water quality management – and installing a direct water supply system, the “Direct Water Supply System Establishment Plan” was developed as part of the Basic Plan for Waterworks Improvement. In September 1999, Seoul amended Article 35 of Seoul’s ordinance on Water Supply and Waterworks Installation in order to establish the “Enforcement Guidelines for Affairs Pertaining to Direct Water Supply.Based on this groundwork, we began pushing through with the direct water supply system in earnest. In addition, we have been running active PR campaigns in an effort to remove completely small water tanks for households by 2014, at the same time mandating the cleaning of small water tanks to manage sanitation as strictly as that of large tanks. At present, small buildings are required to clean the tanks at least semiannually.

Overview of the Policy

<< Removing small rooftop water tanks & switching to the direct water supply system
<< Mandating the cleaning of small water tanks
<< Expanding the use of the direct supply system & prohibiting roof tank installation


As of 2014, Seoul operates the world‘s best water supply system with water supply rate of 100% and revenue water ratio of 94.4%. Optimized for the citizens, the system ensures steady supply of tap water using reservoirs with retention time of over 17 hours, water pressure of 2.5kg/cm2 across the city, and pipelines arranged into blocks to ensure uninterrupted water flow during maintenance works. As conditions for waterworks improved, rooftop water tanks lost their advantages as an important facility that supplied water to small buildings. Instead, roof tanks became a loophole in water quality management, posing a number of problems.
The water quality for general water supply facilities is strictly managed by Seoul because the city as the water service provider owns and maintains such facilities. Nonetheless, there was no mandate regarding the maintenance of roof tanks of small buildings; in some cases, owners or managers of such buildings took sanitary measures only perfunctorily. All these factors contributed to the public distrust in tap water.
In general, large buildings such as apartments, multi-family houses, high-rise buildings, and schools opted for a water supply system that involved tanks. After water is produced at the purification plants, the system first stores it in an underground tank, and then pumps the water all the way up to a roof tank, from which water is supplied to each floor. Note, however, that the system presented several problems. Because tap water sits in tanks for more than 2-3 days, residual chlorine stays at a low level, giving rise to concerns of bacteria and low turbidity caused by foreign particles.
Roof tanks also pose the risk of deteriorating water quality particularly due to its location. Placed outdoors on building rooftops, water tanks become vulnerable to foreign particles that undermine water quality as well as to penetrating sunlight that creates a breeding ground for algae. Even with these problems, issues related to water quality management persisted. Managers/Owners would either perform cleaning works as a mere formality or forego doing them at all since sanitation and maintenance were left to the managers/owners’ discretion, not required.
On the other hand, the direct water supply system supplies healthy and tasty water straight from the purification plants to household consumers without going through tanks. Thus, this system was urgently needed to address public distrust in tap water.

Process of Policy Implementation

Introduction of the direct water supply system
 • 1985 “Direct Water Supply System” employed for the newly built apartment complex in Mokdong as a pilot project
 • 1996 Study on the introduction of the “Direct Water Supply System” initiated by the Seoul Institute
 • 1997 “Direct Water Supply System Establishment Plan” included in the Basic Plan for Waterworks Improvement of Seoul
 • 2001 Set of standards for the “Direct Water Supply System” provided by the Basic Plan for Waterworks Improvement of Seoul
Modifications to the relevant laws and regulations
 • July 31, 1999 Article 12 (Installation of Direct Water Supply Systems) of the Ordinance on Water Supply and Waterworks Installation newly added
 • October 5, 1999 Provision on the “Direct Water Supply System” inserted into the Enforcement Rule of the Ordinance on Water Supply and Waterworks Installation, defining the administrative procedures and buildings that fall under exceptions
 • September 29, 1999 Article 35 of the Ordinance on Water Supply and Waterworks Installation amended
Installation of the direct water supply system
As of 2000, 2,990 buildings employed the direct water supply system following our promotion efforts and test run on 33 general buildings. In 2001, we provided training and education on the direct water supply system, method, effect, and facility details to 1,441 water supply and pipeline companies located in Seoul and distributed newsletters and leaflets to buildings where installation was available. Our strong commitment produced positive results: a total of 35,712 buildings switched to the direct water supply system by 2007.
Complete enumeration survey on the water supply status of small buildings
In 2009, we hired job seekers to conduct a “complete enumeration survey on the water supply status of small buildings.” The survey results revealed that 488,238 small buildings (95.3%) supplied water through the direct system, and that a mere 23,817 (4.7%) small buildings used water tanks.

Details of the Policy

Removal of (small) rooftop water tanks & shift to the direct water supply system
Replacing (small) rooftop water tanks with the direct water supply system does not mean new pipes need to be installed in the building. Rather, the tank pipes, after tank removal, are directly connected to the pipeline of the building.

Between 2010 and 2011, 9,722 buildings voluntarily removed their roof tanks after we informed the building owners and managers of our project to employ the direct water supply system. When the project yielded weak results, the Seoul Metropolitan Government stepped up and allocated its own budget to remove all the small water tanks of low-rise houses. We plan to complete the project for most general buildings by 2014, with the exception of those where the direct supply system is not applicable. For such buildings, routine maintenance is encouraged through PR activities.

Current status of the removal of (small) rooftop water tanks & shift to the direct water supply system

Types of direct water supply system
The direct water supply system has a number of different types, including pure direct system, pressurized direct system, partially direct system, and combined direct system. If pipes provide enough pressure to send water to the rooftop, the pure direct system is installed. High-rise buildings with insufficient pipe pressure choose pressurized or combined direct systems.

Procedures for the installation of the direct water supply system
① Application
 • Those who wish to install direct or pressurized direct water supply system for buildings at least 4 stories high shall submit an application through the online customer center at the website of the Office of Waterworks of the Seoul Metropolitan Government, to customer support divisions at the waterworks offices in the district, or to civil affairs centers at Gu offices.
 • Upon receiving the application, officials shall compare the submitted building information with a building management ledger and a building permit, issue a receipt to the requester, and forward the request to the division in charge.
② Designation of official in charge and site survey
 • The head of the division shall assign an official as appropriate to take charge of the request and conduct an on-site survey.
 • The official in charge shall thoroughly inspect the building in question including the number of floors, distribution pipeline, inlet pipes, diameter of water meters, and water pressure at pipeline intersection points. Subsequently, the official shall write an inspection report and attach a pipeline network map.
③ Decision to install the direct water supply system
 • Within 3 days of the date of receipt, the official shall write a direct supply system report certificate and a direct supply system notice of return of report and record the result on a logbook. The office shall keep the relevant documents after sending them to the requester.
Mandatory cleaning of small water tanks
As for buildings that choose to maintain small water tanks without changing the mode to the direct water supply system, the “law obliges them to clean the tanks” at least semiannually to ensure strict sanitation management.

Following the aforesaid amendment to the ordinance, the law mandates all buildings to clean the water tanks at least semiannually regardless of the tank‘s size. Thus, sanitation for small water tanks is expected to be strengthened to the same level as that of large water tanks.
The table below illustrates the sanitation measures adopted for large and small water tanks.
Cleaning small tanks at least semiannually may seem insufficient compared to the sanitation measures for large tanks. Still, the fact that the measure is institutionalized by Seoul based on the “obligation to clean small water tanks” is significant in itself. We will decide whether to expand the scope of application further based on an analysis of the progress and a long-term review.
We will promote “the obligation to clean small water tanks” - the first of its kind to be implemented in Korea by the Seoul Metropolitan Government - through various media such as 25 Gu office newsletters, town hall meeting newsletters, bills, and electronic signboards. Supervision and monitoring of the implementation will follow suit.

Prohibition on rooftop water tanks
Water tanks became unnecessary for low-rise buildings with 5 stories or less after the establishment of distribution reservoirs and block system. High-rise buildings such as apartments still maintain water tanks, but the technological development allowed them to employ a booster pump system that places the water tank underground instead of on the rooftop.
In case of new buildings, the water supply agreement for building permits requires houses with up to 4 stories and general buildings up to 5 stories high to install the direct water supply system. We inserted a new clause for apartments and general buildings where the direct system cannot be installed to ban rooftop tanks and mandate the use of the booster pump system.

Know-how & Insights

Overcoming the opposition to the direct water supply system
The reasons for opposing the introduction of the direct system varied: overwhelming costs of performing preliminary water supply works for the building (pipe replacement, diameter expansion); lack of will among building owners who experienced no difficulties in using tap water; tank water being used for emergencies or toilets, and; difficulty in obtaining consent from all the residents in case of multi-family houses.

In the end, we overcame the challenges by utilizing the city budget and support and actively persuading those who were against the project.
Robust promotion of the direct water supply system
Through Gu offices, cable TV, and local newspaper companies, we promoted the advantages of the direct water supply system -- which included improved water quality, reduced cleaning expenses and electricity bills, better building appearance, and space saving -- as well as the newly imposed obligation to clean small water tanks at least semiannually starting July 1, 2014. We hired water supply system companies based in Seoul to perform PR activities while making on-site visits to hand out notices and persuaded people.

Policy Outcome & Evaluation

The direct water supply system prevents water pollution because tap water does not stay in tanks for a long time, supplying healthy and tasty water with secured residual chlorine. Furthermore, the space previously taken up by underground tanks, roof tanks, or water supply pumps can be used for other purposes. Maintenance also became cheaper including reduced electricity bills for operating pumps.

Applicability of the Policy

 • By sharing our know-how with local governments where roof tanks are common, such as the Busan Metropolitan City, we can expect a shift to the “direct water supply system” in such districts.
 • We can widely promote the system as a successful policy of Seoul through the Ministry of Environment and the Korea Water and Wastewater Works Association and export it to other countries with high-rise buildings such as Taiwan, Singapore, and Hong Kong.