Nairobi is one of the cities where the world bank has applied the Integrated Urban Water Management approach in design of its assistance. It's one of four cities in Africa, and like other African cities, it stands ahead of major growth. Actually the urban growth in Africa is estimated at 300 million people over the next 15 years. Which is the same as in China. But one of the additional challenges for Nairobi and for all the African cities is that, they have large areas of non-structured development, of slums that also need to be upgraded at the same time as they must receive new migrants from the rural areas. The available water resources within the Nairobi catchment is inadequate for this development that is required. And consequently, the city must look towards not or non-traditional or untraditional water sources, in order to meet the future water demand. It's here that Integrated Urban Water Management comes into play. It basically states that the city should be seen in the perspective of its catchment and other processes and the plain traditional urban water management of water supply and sewerage and waste water treatment, should be taken into account. If you look at the development of a city like Nairobi, of the water supply, then it can be done using traditional sources. But, of course, it is costly, and a lot of water is wasted in the process. So a lot of the value of a resource is lost. It is possible, but it will require interface and transfer from neighboring catchments. And these neighboring catchments, they are not always happy to give up their water resource for the further development of the main city. Furthermore, traditional water sources, rivers and lakes, they are subject to the variation of climate change, which imposes a risk that we cannot quantify at the present time. If you look at instead at the development taking Integrated Urban Water Management into account, then actually the first thing that you could do is to look at the water tariff is to introduce water resources demand management, typically by an increase of the water tariff. So that the water supply, waste water becomes full-cost recovery from water fees. And this is an administrative measure that doesn't cost very much. The next step that you can look at is the leakage detection. In most major cities, especially in Africa, the leakage from the water distribution network is the range of 30 to 40%. There are examples in other places of the workplace. Half of the processed water that is lost on its way from water treatment plants to the consumer. And also here, it is relatively cheap. Exercise to identify where are the leaks and to repair them. After this, you can then start to develop the traditional water resources or you can develop some of the untraditional water resources. Applying the IUWM, means that we can postpone investment in heavy infrastructure for about eight to ten years. And this is also valuable, when you have to save money for future development. It doesn't cost very much to build up a little extra the traditional, or existing water sources. But when you come to untraditional things, like storm water recovery, use of waste water, reuse of waste water, then the marginal costs rises very much, and from say about less than $1 to up to $3 per cubic meter. Conclusion. That when you have explored it, we can save the low hanging fruits. Then, you'll see a very, very steep increase in marginal cost of further water resource development.