Water Distribution : Revenue Water Ratio & Leak Management
Achieving the Highest Revenue Water Ratio in the World
The Office of Waterworks and its branch offices are public enterprises that have two tasks: to serve public good by supplying clean, safe water and to rationalize business management. The best way to achieve the latter is to improve the revenue water ratio (RWR), which cuts production cost and other expenses.
In 1989 when the Office of Waterworks of the Seoul Metropolitan Government was founded, RWR stood at a mere 55.2%. Our dedicated efforts for the past 25 years greatly rationalized management, hiking up RWR to as much as 94.4% in 2013.
Putting the impact of improved RWR enabled by rationalized management into context, the amount of water saved between 1990~2013 was 7,500,000,000nf, which was worth approximately KRW 4.2 trillion. This is equivalent to the amount used by 10 million Seoul citizens for 6~7 years. Leak cases also decreased by 725,998 (82.5%), saving KRW 1.8 trillion in budget.
As we became capable of cutting the amount of tap water production, we closed down 4 of our 10 purification plants (capacity of 7,300,000m3 per day); thus operating only 6 plants at present. The closed plant sites have been transformed into parks for citizens, contributing to the improvement of their quality of life and local economic development.
Overview of the Policy
<< Scientific and systematic IT-based leak detection
<< Minimum night flow (MNF) measurement
<< Old water pipe maintenance
<< Establishment of gravity flow system using reservoirs
<< Scientific management of water flow through the flow monitoring system
<< Sharing of RWR know-how with other local governments and providing consulting
Ever since the Office of Waterworks was founded in November 1989, improving RWR has been a necessary groundwork for us to achieve independent management
RWR refers to the percentage of billed water as a share of net water produced in purification plants. Thus, higher RWR means less water loss during the process of supplying tap water or, simply put, less leaks. Therefore, increased RWR allows the reduced production of tap water. This in turn brings down expenses for raw water purchases, chemicals, and power, thereby improving waterworks management. The benefits from such advanced management eventually go to the citizens.
Process of Policy Implementation
Phase 1: Initial phase of RWR improvement (1989 - 1995)
• Office of Waterworks established (November 21, 1989)
• District-level flow meter installed for the first time (1990s)
• Intensive maintenance of old water distribution/supply pipes (4,200km) (1991~1993)
• Measuring system using district flow meter fully put in place at each of the waterworks offices (1995)
Phase 2: Development phase of RWR improvement (1996 - 1999)
• RWR improvement team launched (October 12, 1998)
• District-level measurement of supplied amount and RWR initiated (1996 - 1997)
• Proper meters with smaller diameter installed, replaced inappropriate meters (1996 - 2000)
• MNF measured by dividing the Seoul pipeline network into 2,037 small blocks (1998)
• Official district-level RWR statistics produced for the first time (1998)
• Intensive management of waterworks facilities at the redevelopment and reconstruction sites (from 1999)
Phase 3: Settlement phase of RWR improvement (2000 - present)
• Shifted to indirect supply system after reservoir establishment (913,000nf) (2000 - 2003)
• Office reshuffled, RWR management responsibility transferred from waterworks task force to RWR division (January 8, 2001)
• Meter-reading works entrusted to private entities (July 22, 2001)
• Appropriate pressure of booster pumps managed in each time period (inverter) (from 2002)
• Systematic management of disused pipes (359km) (from 2003)
• Block-level RWR managed after introducing the medium block system (from 2004)
• Scientific leak detection started using the multi-point leak noise correlation system (from 2004)
• Supplied amount analyzed, flow controlled through the flow monitoring system (from 2005)
Details of the Policy
Scientific and systematic IT-based leak detection
Leak detection constitutes a crucial part in waterworks especially for RWR improvement.
To ensure systematic leak detection, Seoul divided the city‘s waterworks pipeline into 2,037 small blocks and sought to detect underground leaks focusing on those that recorded the most number of leak cases over the past three years based on the GIS system.
Since 1999, we have hired 60 - 70 leak detection specialists as fixed-term employees to enhance effectiveness and create jobs.
In 2004, we introduced the latest technological device to make leak detection more precise: the multi-point leak noise correlation system, which offers a comprehensive solution. This device collects leak noises through the high-sensitivity sound sensors attached on gate valves, fire hydrant, and meters. Using the installed program, the system conducts complete analysis of noises and pinpoints the locations of all leaks with high precision. These points are digitized and presented in 3D graphs.
As for the number of leaks detected every year, it was 16,175 in 2004 but dropped dramatically to 2,601 in 2013 when maintenance of water distribution/supply pipes and disused pipes was successfully completed. The number is expected to go down further in the future.
Minimum night flow (MNF) measurement
Minimum night flow refers to the minimum amount of water flow in a given block during the period of the lowest tap water consumption (midnight - 4 am on average). MNF measurement is designed to avoid leaks by evaluating whether a block exceeds the allowable leak, in which case active leak detection is initiated.
From 1998, we kept the leaks in all 2,037 small blocks in Seoul below the allowable leak limit (1m3/hr.km). From 2003 to 2005, we reinforced our detection work and set the allowable leak limit between 0.5m3/hr.km and 1m3/hr.km depending on the waterworks conditions of the blocks. Since 2006, the work has been performed partially on blocks presumed to have more leaks (allowable leak limit: 2.0m3/hr.km).
Old water pipe maintenance
Old water pipes refer to non-corrosion-resistant pipes that corroded both inside and outside after being used for a long time. These pipes result in frequent leaks, and the rust from corroded pipes breaks free and causes red water. Examples of non-corrosion-resistant pipes are as follows:
• Pipes made of gray case iron, steel, PVC, and galvanized steel and buried before 1984
• Corrosion-resistant pipes that have been in use for over 40 years and with frequent leaks
The maintenance of old pipes prevented tap water pollution and secured the quality of water during the entire process of supplying water to household faucets. Leaks from old pipes were also prevented in advance, which led to higher RWR. The pipe network, which changed from the branching system to the circular block system, also realized a more stable water supply system.
Over the 22-year period between 1962 and 1983, the old pipe maintenance project replaced around 1,821km of old pipes, which cost KRW 36.6 billion. In 1984, we performed extensive maintenance works on water distribution/supply pipes by formulating a comprehensive maintenance plan. As of 2013, we completed refurbishing 13,192km (96.5%) out of the 13,668km pipeline. The goal of this project is to finish maintenance for the remaining 476km by 2018.
Gravity flow system establishment using reservoirs
We replaced the supply system that delivers tap water straight from purification plants or pressurizing stations with a gravity flow supply system that involves reservoirs. Through such change, the water supply system became more stable with less pressure-induced leaks and even pressure maintained 24/7.
To date, there are 104 reservoirs constructed and operated, with capacity of 2.38 million and retention time of around 16 hours.
Scientific management of water flow through the flow monitoring system
The water flow monitoring system performs comprehensive management of the collected real-time data on water flow and pressure created during the supply process for systematic flow control using the accumulated statistical information. The system employs a unique web feature that allows all officials at the Office of Waterworks to search for the necessary information at any time with their personal computers.
The basis of the monitoring system consists of 435 flow meters for water intake and transmission, for districts and medium blocks, and for pressurizing stations and reservoirs. To obtain an accurate amount of water supply, we have capped the margin of error at ±0.5% (Ministry of Environment standard: ±2.0%).
By utilizing the flow monitoring system, we analyze the daily supply of water from each source water. If sharp increase or decrease is detected, we identify the cause immediately to minimize leaks.
Sharing of RWR know-how with other local municipalities and providing consulting
The Office of Waterworks and the Korea Water and Wastewater Works Association have provided joint consulting services to local municipalities with low RWR to share know-how and technologies.
Since 2010, we have visited seven local cities to support them with our know-how on RWR improvement, thereby contributing significantly to the development of waterworks in the local districts.
The major items that we set forth include detecting leaks, offering tailored solutions for RWR improvement, and educating the relevant officials on management methods to raise the ratio.
Know-hows & Insights
Underground Leak Detection
• Minimum flow measurement
A team of 4-5 workers (daily workers included) conducts (01:00 - 04:00) water leak detection for a day; 1 person measures the minimum flow at the flow meter-installed area, with the remaining 3-4 workers detecting the leaks with listening sticks, visual inspection of roads, and water meter boxes.
• Leak detection for drain pipeline
Leak detection teams each consisting of 3-4 workers performed daily leak visual inspection on water leaks from medium blocks with low RWR to drain pipelines as well as checking of the maintenance status of waterworks pipelines. In principle, detection is to be conducted during daytime; note, however, that certain sections require nighttime inspections. Under such circumstances, we plan for concentrated detection works so that the process could be completed within 1-2 days and to save cost.
• Acoustic water leak detection
For acoustic water leak detection, we first prioritized the water distribution/supply pipes near medium blocks with poor RWR by marking the pipes with diameter of 400mm or more on a detection plan drawing of each district (1/10,000 - 1/25,000). After performing detection works on the entire pipeline of the waterworks office following the order of priority as well as visually checking for leaks inside the drain pipes, we conducted precise detections on sections that showed signs of leaks.
With regard to sections where water flow changes, we continue to check for leak noises (vibration); if any noise if found, then we start precise water leak detection using acoustic detectors and inspect the interior of drain pipelines.
• Multi-point leak detection
Also known as a comprehensive system for leak diagnosis (SOUNDSENS), the system collects leak noises through high-sensitivity sound sensors installed on gate valves, fire hydrant, and water meters of water distribution/supply pipes. It then pins down the location by analyzing the collected noises using a program and displays the results in digitized version and 3D graphs.
• MNF measurement
Minimum night flow refers to the minimum amount of water flow in a given block during the period when tap water consumption is lowest (midnight - 4 am on average). MNF measurement is a method of avoiding leaks by actively performing leak detection if the block exceeds the minimum flow.
• Old water distribution/supply pipes maintenance
• Real-time management of water supply
Policy Outcome & Evaluation
As indicated in the tables below, Seoul’s RWR in December 2013 stood at 94.4%, which increased drastically from 1999 and onward, after showing minimal upward trend between 1991 and 1998. This achievement, along with reduced leaks, has vastly improved the management of the office.
Production facilities and improved highland pipes completely resolved the issue of water interruptions. Major policy tasks for waterworks administration also shifted from supply-centered policies to management-centered ones, with the aim of advancing management through better water quality and higher RWR.
In the past, the city council and civic groups have repeatedly demanded measures to address low RWR. Today, big cities of the country not only maintain one of the highest RWRs; they are also on a par with advanced nations across the world.
Applicability of the Policy
Small and mid-sized municipalities in Korea and developing countries with low RWR can benchmark the method to improve their RWR. This method can be particularly effective on hilly areas.
How do you calculate RWR?
The ratio of billed water to net water produced at purification plants
→ RWR(%) = Amount of revenue water / Total amount of supplied water x 100
※ Revenue water: Billed water