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Municipal wastewater: from production to use

The CGIAR Research Programme on Water, Land and Ecosystems, led by the International Water Management Institute (IWMI), and the Land and Water Division of FAO are collaborating to collect, analyze and validate the best available data on municipal wastewater production, collection, treatment, discharge and direct use for irrigation purposes. The results of this collaboration are available in AQUASTAT, also announced on IWMI’s website.

While other existing wastewater databases often focus on percentage of sanitation coverage or pollution loads, AQUASTAT focuses on annual volumes at national level. The reason for choosing volume as the parameter is to facilitate the integration of these data in the water resources and use accounts in the different countries.

The  diagram below illustrates the flow of wastewater from production to use. The variables squared in blue are available in the AQUASTAT country database. Th e variables (1)-(11) can be accessed under the category “Wastewater” and have the unit km3/year or 10^9 m3/ year, except for variable (4), which refers to the number of treatment facilities. The variables (12)-(13) can be accessed under the category “Irrigation and drainage development”, sub-category “Area equipped for irrigation by source of water”, and have the unit 1000 ha. Information on the level of treatment is, if available, provided in the metadata of the variable “Treated municipal wastewater” (3).

Definition of terms and variables

Definitions of wastewater-related terms and variables are included in the AQUASTAT glossary and can be consulted by clicking on the names below (on our virtual edition from our website www.afriwater.org). Th e fi gures between square brackets refer to the fi gures between square brackets in the figure above.

• Wastewater
• Produced municipal wastewater (1)
• Collected municipal wastewater (2)
• Municipal wastewater treatment facility
• Treated municipal wastewater (3)
• Number of municipal wastewater treatment facilities (4)
• Capacity of municipal wastewater treatment facilities (5)
• Not treated municipal wastewater (6)
• Treated municipal wastewater discharged (secondary water) (7)
• Not treated municipal wastewater discharged (secondary water) (8)
• Direct use of treated municipal wastewater (9)
• Direct use of treated municipal wastewater for
irrigation (10)
• Direct use of not treated municipal wastewater for irrigation (11)
• Area equipped for irrigation by direct use of treated wastewater (12)
• Area equipped for irrigation by direct use of not treated wastewater (13)

Note: when clicking on “View data for this variable in the AQUASTAT Database” in the description of the variable in the glossary, an AQUASTAT database results page will appear containing all data available for this variable.

Data sources, selection and validation

Data collection takes place through review of country briefs and national reports, databases, technical reports, peer-reviewed publications, information provided by national experts, presentations from national authorities in seminars, Internet search, etc.

Since data come from many diff erent sources, inconsistencies may occur over the course of time.Therefore, each time new data become available a detailed review and validation of all data, both new ones obtained and the ones already available in the database, is essential.

Data is validated in relation to a time span from 1958 to 2012, based on the assumption that mainly the annual volume of wastewater produced, but probably also the annual volume collected, treated, discharged or directly used should - unless justifi ed, such as for example due to contraction in the municipal population growth - show incremental increase as water use would rise over time.

Data is also validated in relation to various stages of the wastewater cycle, i.e. wastewater production (assumed to be the highest volume), wastewater collection, treatment and direct use (lowest volume of water). For more information on the rationale, method, sources and setup of the this global wastewater database, see the methodological paper.




Current Issue: Africa Water & Sanitation & Hygiene March-April 2017 Vol.12 No.2