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Wastewater use in irrigated agriculture: closing the rural-urban-rural water loop. Presented at Departmental Seminar Series (Soil, Water & Environmental Science), University of Arizona, 19 February 2007. Wastewater Use in Irrigated Agriculture: Closing the Rural-Urban-Rural Water Loop

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Wastewater use in irrigated agriculture: closing the rural-urban-rural water loop

Presented at Departmental Seminar Series (Soil, Water & Environmental Science), University of Arizona, 19 February 2007

Wastewater Use in Irrigated Agriculture:

Closing the Rural-Urban-Rural Water Loop

Christopher Scott

Udall Center for Studies in Public Policy, and

Dept. Geography & Regional Development

University of Arizona

Scarcity & Competition for Water

  • Declining allocations of water to agriculture

  • Rapid urban growth a global phenomenon

  • Water productivity in agriculture rising (“more crop per drop”)

  • Agriculture increasingly adapting to the use of poorer quality water for irrigation

Sobering Demographics

  • 880 million additional population by 2015, virtually all in developing countries.

  • After 2015, all worldwide growth in population will take place in developing country cities.

Urban Explosion

  • India will soon cross the 50-50 urban-rural population threshold… 750 million urban Indians by 2050.

  • China is actively planning for cities each with more than 100 million population.

  • Africa’s urban population growth rates among the highest in the world.

  • Latin America has been predominantly urban for generations.

Urban Water Supply Growth

Millennium Development Goals face resource constraints (water, investment). Progress towards sanitation goals lagging behind water supply; therefore, wastewater management is critical.


  • Wastewater = partially treated or untreated urban sewage

  • Effluent = treated to secondary or tertiary levels (with or without disinfection)

Rural-Urban-Rural Water Loop

  • Transfer of water from agriculture to cities

    • Physically, often entails inter-basin transfers

    • Water rights, property regime, economic issues

  • Urban use, quality degradation & depletion

    • Salinity load, even with (because of?) treatment

    • Public health risk (consumers and producers)

  • Agricultural end use of wastewater/ effluent

    • Adapt to quality (nutrients, salinity)

    • Adapt to timing (uniform throughout year)

Rural-Urban-Rural Loop Typology

Hyderabad, India

Sampling Transects

III – rural (25 – 40 km)

II – periurban (10 – 25 km)

I – urban (0 – 10 km)

Hyderabad Water Footprint

Hyderabad Water Supply/ Demand

Wastewater Biogeochemistry

  • Microbial attenuation and infection

    • Coliform die-off

    • Nematode (hookworm) egg deposition

  • Heavy metals attenuation (& uptake?)

    • Deposition, re-suspension

  • Nutrient attenuation – plant uptake, eutrophicn.

  • Dissolved solids concentration, deposition

    • Irrigation diversion, evaporation, return flow

+40 Km


Coliforms in WastewaterDec. 03 – Jan. 05 (red squares = mean value)

Nematode Eggs in Wastewater

Nematode Prevalence in Farmers

Sediment Sampling

Mean egg load per 1 kg of sediment:

410,000 (SD: 240,000)







High Court

Heavy Metals in Sediment

Source: Gerwe, Caroline. An Assessment of Heavy Metals Contamination in the Wastewater-Irrigated Area of the Musi River

Dissolved Nitrogen

Dissolved Oxygen

Total Dissolved Solids

TDS Seasonal Variation

TDS Conceptual Model

Irrigation Adapts to Constant Flow

Mexico City Water Footprint


Mexico City Wastewater Sources/Fate

Tula Irrigation District

Nutrient Uptake, Salt Concentration

Monterrey-Bajo Río San Juan Swap

Falcon Reservoir

Marte R. Gómez Reservoir

McAllen, Texas

Bajo Río San Juan Irrigation District


El Cuchillo Reservoir


El Cuchillo

  • Constructed in 1993

  • Supplies 5 m3/s to Monterrey (to be increased to

10 m3/s)

  • MR Gómez reservoir impacts

Negotiated Settlement

  • 9 Oct. 1989 – Monterrey, federal and Nuevo León governments agree to finance and construct El Cuchillo dam

  • 6 Sept. 1990 –Tamaulipas, federal and Nuevo León governments agree to “rationalize” water use, preserve multiple uses of BRSJ irrigation water

Effluent – the Bargaining Chip

  • Federal CNA allocates 189 MCM (6 m3/s) of effluent from Monterrey to BRSJ irrigators

  • Nuevo León assumes responsibility and cost of treatment in compliance with federal water quality standards

  • Rehabilitation of the Anzaldúas-Rhode pumping station on the Río Bravo

  • Relocation of downstream Tamaulipas urban water demand from MR Gómez reservoir (Rhode canal)

BRSJ Irrigation Water Productivity

BRSJ Irrigation Efficiency

But, growing upstream demand and capture of wastewater; will need to pipe it 100+ km.

Wastewater Use: Conclusions

  • Urban growth + high tertiary treatment costs = increasing agricultural reuse

  • Promote beneficial agricultural reuse

  • Mitigate health and environmental risk

Risk Mitigation

  • Secondary treatment (biosolids handling enforcement is essential)

  • Application method to limit irrigators’ exposure

  • Market wash water and handling

  • Crop restrictions – non-edible and fodder. Limit fresh produce irrigation, e.g.:

Treatment for Compliance

  • WHO - 103 faecal coliforms/100 ml

    • Cost of treating raw sewage used for direct irrigation to meet WHO standard is approx US$125 per case of infection (of hepatitis, rotavirus, cholera, or typhoid) prevented (Fattal, Shuval, Laempert, 2004).

  • USEPA – zero incremental risk

    • Incremental cost of further treating wastewater from WHO to USEPA standard approx. US$450,000 per case of infection prevented (Fattal, Shuval, Laempert, 2004).

Policy Implications

  • Planned reuse offers no easy solutions

  • Key to success are:

    • coherent legal and institutional framework

    • coordination of multiple government agencies

    • flexible application of the ‘polluter pays’ principle

    • extension to farmers of appropriate practices for wastewater use

    • public awareness campaigns to build social acceptability for reuse

Wastewater Use in Irrigated Agriculture

  • http://www.cabi.org/bk_BookDisplay.asp?PID=1785

  • http://www.idrc.ca/en/ev-31595-201-1-DO_TOPIC.html

  • Introduction: management challenges

  • Typology and global assessment

  • Livelihoods the key driver

  • WHO health guidelines

  • Cost of guidelines compliance











Case Studies in the Book

Formal programs of planned reuse with treatment

Thank you.

Christopher Scott




  • Stephanie Buechler, UA Bureau of Applied Research in Anthropology

  • Pay Drechsel, International Water Management Institute, Ghana

  • Jeroen Ensink, London School of Hygiene and Tropical Medicine

  • Naser Faruqui, International Development Research Centre

  • Francisco Flores, Cornell University

  • Jesús R. Gastélum, UA Dept. of Civil Engineering

  • Liqa Raschid, International Water Management Institute

  • Daan van Rooijen, International Water Management Institute, Ghana

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