Could we have the figures for leaking sewers, please?

Today, the concept of non-revenue water or NRW has become well-established for judging the efficiency of water utilities. The difference between water which is supplied to the network and the water which is billed denotes a loss of revenue that has come to be called NRW. Experts rightly declare that it is a misleading term and IWA has urged the use of Infrastructure Leakage Index or ILI to describe the efficiency of the real loss management of water utilities.

While ILI might need some time to take root, we do have the NRW percentages for countries around the world, for whatever they are worth. Thus, there is Malaysia with 41%, India with 40%, France with 27% (yes, the home of Veolia and Suez), Spain with 25%, UK with 23%, China with 22%, US with 11%, Germany with 8% and the only redeeming figure for Asia – Singapore with 5%.

The figures for NRW might be debated but we at least have some figures. What’s surprising is that there is little talk about the extent of losses from sewers. Or maybe it is not all that surprising since sewage has even lesser or nil value compared to the little value that is placed on water. People hardly pay for sewage treatment (if it is treated) and even if 20% of sewage is lost in transit, it will not set alarm bells ringing, at least in Asian countries.

There can be absolutely no doubt that sewers must be leaking everywhere, even if not as much as water pipes, which are pressurised. After all, sewers are not manufactured using vastly different technologies or skills. Sewers are mostly made of materials such as reinforced concrete, ductile iron, plastics (for small diameter uses) and FRP. They could leak for various reasons such as poor laying, third party damage, service damage and operational damage.

Even though sewers are known to have self-sealing properties, exfiltration from sewers could have serious consequences on surrounding soils and groundwater sources. With urban sewage nowadays containing not just the usual microorganisms but pharmaceuticals, detergents, fragrances, hormones, household cleaners and other contaminants, the risks today are far more than ever before. It will take years before studies can conclusively establish the link between leaking sewers and diseases, but should governments wait for that long?

In today’s age of advanced science, it is possible to use a robot to inspect sewers for defects. Advanced methods of sewer rehabilitation and replacement are also available, once the defective sewers are identified.

However, what is missing is data at national and international levels regarding the extent of leakage from sewers. Agreed that it is not easy to measure, since pipes buried underground always pose a problem. But modern science is coming up with such ingenious, indirect methods of detecting and measuring leakages that there can be no excuse for not investigating an issue that is so crucial. For example, studies have indicated that artificial tracers can be added to sewage, and if the sewer is leaking, a part of the added tracer would be lost with the leaking sewage, which can be directly linked to exfiltration.

In those parts of the world where water reuse has become popular, perhaps there is a greater concern to prevent leaking sewers. In Singapore, for instance where NEWater or treated used water is supplied to industries, it would make little sense to lose sewage through leaks. If the nutrient value of sewage is taken into account, it becomes even more valuable.

It is still premature to think of Non-Revenue Sewage but can we at least know how much our sewers leak?

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