Water management

The data gap

A comprehensive search identifies a global dearth of data on the generation, treatment and use of wastewater. Remedying this situation will help policy-makers to better legislate for the management of this precious resource.

An interesting but worrying analysis of the situation of wastewater assessment around the world is presented by Sato et al.1 in Agricultural Water Management. In a thorough review of different sources of information, including scientific literature and government reports, from a spectrum of countries representing different regions and socio-economic conditions, the authors reveal that data on the generation, treatment and use of wastewater around the world are scarce and poorly reported.

Of the 181 countries assessed in the study, Sato and colleagues found that data were available on all three aspects of wastewater for only 55, and that no information at all was available from 57 countries. Only 37% of the available data were reported in the period 2008–12. Although many water-management experts are already well aware of this state of affairs, the authors' findings demonstrate to a broader audience how policy-makers around the world have, to a large extent, failed to implement policies to gather data on wastewater. This is disappointing, because such information is crucial to making informed decisions on several issues, including pollution management and how the use of wastewater could contribute to addressing water-scarcity issues and the potential threats of climate change in some regions. Water, in contrast to many other natural resources, is renewable, but in an era in which the recycling of solid waste and used materials is strongly promoted in greener societies, the lack of discussion about wastewater generation, and especially its reuse, is remarkable.

It is worth considering some possible 'invisible' explanations for the lack of data. One is an inherent rejection of wastewater, owing to its association with water-borne diseases. Another is that, unlike the clean water that users have to pay for, wastewater may be considered to be without value, meaning that there is little interest in measuring what happens to it. But in a world in which the demand for this finite resource is increasing, wastewater — or used water, as I prefer to call it — should also be given a value and be measured. This is starting to happen in parts of the world where water is scarce and farmers, for example, must pay for wastewater.

Indeed, although many policy-makers have yet to adequately consider the potential of used water, the opposite is true of many farmers (Fig. 1). Both treated and untreated wastewater is already used for irrigation in many regions, and this form of water reuse is increasing, although Sato and colleagues' study fails to catch this trend because it is based on data not older than 2000. By reusing water instead of relying on rain-fed irrigation, farmers may be able to sow three or four crops per year, rather than only one or two. Used water also contains nutrients, such as nitrogen, phosphorus and organic matter, that enrich the soil and increase crop yields. In fact, the presence of such usable compounds in wastewater may prove to be a motive for enhancing water-reuse practices. Natural reserves of phosphorus are rapidly declining, and the phosphorus industry has recently called for action to save and recycle this fertilizer2. Another advantage of the reuse of water for irrigation is that it contributes to the recharging of aquifers, and thereby becomes a new source of usable water.

Figure 1: Renewable resource.


Wastewater is increasingly being used for irrigation purposes, but a lack of data on wastewater generation, treatment and use1 is hampering the development of policies regarding this resource.

“The use of untreated wastewater for agriculture is a public-health concern.”

Thus, the attractions of using wastewater, particularly for farmers in low-income regions, are obvious. But in many cases water is being reused without proper policies and practices. Sato et al. find that high-income countries, on average, treat 70% of their wastewater, but this figure drops to 8% in low-income countries, and the reuse of untreated wastewater has been estimated3 to be about 5–8 times greater than that of treated used water. The use of untreated wastewater for agriculture is a public-health concern: wastewater can function as a vector for diarrhoeal diseases when polluted water is ingested with crops that are consumed raw.

Although irrigation is a primary focus of water-reuse issues, wastewater-management considerations should not be confined to agricultural areas. Cities may make up tiny areas of our planet, but they demand large quantities of water and food, and produce a vast amount of used water. Much of this water — and the nutrients it contains — could be reclaimed to help to produce food for urban dwellers. Methods to treat water are becoming available that cost less than conventional methods and also provide the ability to recycle nutrients4. Thus, researchers are developing the means to establish site-specific and cost-effective approaches to water reuse, but the data gap must be closed before such policies can be effectively designed.


  1. 1

    Sato, T., Qadir, M., Yamamoto, S., Endo, T. & Zahoor, A. Agric. Water Mgmt 130, 1–13 (2013).

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    Cordell, D., Drangert, J.-O. & White, S. Glob. Environ. Change 19, 292–305 (2009).

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    Jiménez, B. & Asano, T. (eds) in Water Reuse: An International Survey of Current Practice, Issues and Needs 3–26 (IWA, 2008).

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    Jiménez, B., Mara, D., Carr, R. & Brissaud, F. in Wastewater Irrigation and Health: Assessing and Mitigating Risk in Low-income Countries (eds Dreschel, P. et al.) 149–170 (Earthscan, 2010).

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Correspondence to Blanca Jiménez Cisneros.

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Cisneros, B. The data gap. Nature 502, 633–634 (2013). https://doi.org/10.1038/502633a

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