< MODULE 3 >

The next topic is Revenued Water Ratio. Revenued Water Ratio means the ratio of the volume of water paid by the citizens, customers, to the volume of water that is produced and supplied to the citizens.

Academically we use Non-revenued Water, NRW, or Unaccounted for Water, but in Seoul we use RWR, Revenued Water Ratio, to evaluate the efficiency of the system.

The special organization for drinking water in Seoul, which is the office of the waterworks, started in 1989. When the organization started, RWR of Seoul, Revenued Water Ratio of Seoul, was 55 percent.

Which means the other 45 percent of water is gone between the production and supply, such as leaking, or stealing, or everything. But the RWR of Seoul has increased dramatically during 1990s and 2000s, and the RWR in 2015 was 96 percent.

It’s the world’s highest RWR. Again, this is timeline with the production capacity which is the blue line and the income the GDP per capita is purple line, and green dotted line is RWR.

As we discussed before, the Korean economy and population of grew rapidly during the 60s and 70s and the drinking water production capacity also increased rapidly during that time.

But as we can see the RWR during that time is steady, around 55 percent, which means we focused on the amount of water produced and delivered to the citizens, not the efficiency of the system.

But after 1990s and 2000s, when the capacity of production was stabilized with the population, the city could focus on the efficiency of the system so we could increase RWR rapidly after 1990s.

So I’d like to discuss how we could increase the RWR. One of the approaches to increase RWR was leak management. In 1989, the 60,000 cases of leak were detected in our waterworks system, but with the tight leak management we could reduce the leak case from 60,000 to 10,000 in 2015.

So that’s one of the approaches to increase RWR from 55 to 96 percent. Another approach is pressure control. As we discussed before we have many hills and mountains in Seoul area, the city used that mountain as reservoir. We installed the big reservoir in a mountain. The size of the reservoir is huge, so you can imagine it as a building on a mountain.

The system goes like this: the water produced at the plant is pumped to the local reservoir, the city has 32 local reservoirs, and the water in the local reservoirs is pumped to the first reservoir at the higher altitude, about 30 meters difference, and water in first reservoir pumped to the second, second to the third, goes like this.

But we use cheaper electricity at night time to pump water from local reservoir to first and second so we could reduce the pumping cost. And also the community located here gets water from the third reservoir, community here gets water from the second so we could control the water pressure, which means we could reduce the leak by controlling the water pressure with the reservoir system.

Another approach is the block system. Before we had circular block system, we had distribution system like this. We called that tree-shaped distribution system. In this system the water at the extremity can deteriorate the water quality, and also it’s not circular so we could not control the leak and flow efficiently with this system.

So the city changed the distributions system into a circular one. We have small blocks, so we made this small blocks and city of Seoul has 2,000 small blocks for the distribution system so we could control the leak and flow and pressure block by block.

So it’s very efficient because we divided the system into small blocks and we can control it easily. The block system is not flat.As we discussed before, the water pressure is related with the elevation so the block system is constructed considering the elevation of the each block.

And we use noise detection to find out the leaking point, and this leak detection is carried out block by block.The city installed water flow monitoring system all around Seoul so we can check the water flow differences and abnormality through the system.

And another and the best approach to increase RWR is replacing the old pipes. Since we started the project in 1989, the city replaced about 97 percent of old pipes in 2015. As we replace more and more old pipe into new one the RWR increased rapidly.