This document discusses the challenges of rapid urbanization for water management. More than half the world's population now lives in urban areas, with most growth occurring in developing country cities that gain an average of 5 million new residents per month. As cities expand, they place increasing demands on water sources, often drawing water from farther distances and depleting groundwater reserves. Cities also generate large volumes of wastewater but sanitation infrastructure is lacking, leading to widespread water pollution. The document argues that cities should be viewed not just as "sinks" but also potential "sponges" if wastewater is safely reused. Closing nutrient and water loops between cities and surrounding agricultural areas could help mitigate environmental impacts while improving resource use.

1. Cities and Water:
Sinks or Sponges?
16th International River Symposium
Brisbane, 23 September 2013
Jeremy Bird
International Water Management Institute

2. • More than half of
the world’s
population lives in
urban areas.
• Urban growth is
most rapid in
developing
countries: cities
gain an average of
5 million residents
each month.
• There are 23
megacities,
compared to 2 in
1970. By 2025,
there will be 37.
Percentage of urban population and agglomerations by size class, 2011
Percentage of urban population and agglomerations by size class, 2025
Source: United Nations, Department of Economic and Social
Affairs, Population Division: World Urbanization Prospects,
the 2011 Revision. New York 2012

3. What is urban?
What is rural?
Accra:
the administrative
boundary is
outpaced by urban
sprawl

4. Map of
population
density
South Asia exemplifies urbanization challenges and
rural-urban tensions
http://pricetags.files.wordpress.com/2013/03/pop-density.jpg

5. Example: New Delhi
1974 1999 2013

7. Time for a new approach….
“For most of the last century, economic growth was
fuelled by what seemed to be a certain truth: the
abundance of natural resources. We mined our way to
growth. We burned our way to prosperity. We believed in
consumption without consequences. Those days are
gone….. Over time, that model is a recipe for national
disaster. It is a global suicide pact.”
United Nations Secretary General Ban Ki-Moon,
World Economic Forum 29th January 2012.

8. Urban unit
• Supply infrastructure
• Sewage infrastructure
Wastewater disposal
• Receiving water bodies
• Use in irrigated agriculture
Water source
• River
• Groundwater
• Reservoir
• Rainfall
wastewater treatment?
Sink and Sponge
Source: van Rooijen, D.J.; Biggs, T.W.; Smout, I.; Drechsel, P. 2010. Urban growth, wastewater production and use in irrigated agriculture:
A comparative study of Accra, Addis Ababa and Hyderabad. Irrigation and Drainage Systems 24(1-2): 53-64

9. Urban expansion, Hyderabad, India
Source: Wikimedia Commons

10. Pulling water in from an increasing distance
Hyderabad, India
Krishna River
Himayat Sagar
Osman Sagar
GW
Musi River
GW – Ground Water
NJS – Nagarjuna Sagar reservoir
Hyderabad
Waste water irrigation
industry
Godavari Basin
Krishna Basin
NJS
Musi River
P ET
Manjira
Singur
Godavari River water
W
ater pum
ped
Waterpumped
Source: van Rooijen, D.; Turral, H.; Biggs, T.W. 2005. Sponge city: Water balance of mega-city
water use and wastewater use in Hyderabad, India. Irrigation and Drainage 54: 81-91.

11. Change in water sources to satisfy urban needs
Hyderabad Water Supplies and Demands
Osman Sagar Himayat Sagar
Ground Water
Singur
Manjira
Krishna river
Godavari
extra needed
(demand - total supply)
0
10
20
30
40
50
60
70
80
90
100
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
time (years)
MillionCubicMetersperMonth
Source:
Van Rooijen et al., 2005

12. Informal water markets on the increase
• No Indian city has a 24/7
water supply.
• Demand for tanker supply
on the increase.
• Most affected are
peri-urban areas where
groundwater tables are
dropping.
Photo by Akshay Davis

13. Groundwater
extraction in
India:
Urban needs add
to existing stress
from agricultural
use

15. Examples of water transfers exist
…as allocation to
agriculture reduced
and transferred to
urban use
Agricultural
production levels
maintained…

16. Reflections : Cities as a water sink
• Footprint of urban expansion on water for irrigation can be
extensive - depends on water source (surface water –
groundwater; basin diversion, etc.) and response measures to
incentivize water productivity gains
– cities like Chennai and examples from China show a major impact on
peri-urban water needs.
• Rapidly urbanizing cities need a shift to more pro-active, cross-
sectoral planning capacity, e.g:
– a broad multi-sector approach: managing water transfers, demand
management, rainwater harvesting, conjunctive use, etc.
– explore downstream irrigation opportunities from a more continuous
supply of wastewater and increased storm runoff
– promote health safeguards for wastewater re-use

17. What happens to the urban ‘return’ flow?
Urban unit
Wastewater
disposal
Water source
wastewater treatment?

18. In most cities in sub-Saharan Africa, S. Asia and SE Asia, population
growth has outpaced the development of sanitation infrastructure,
making the management of urban waste, human excreta and
wastewater ineffective.

19. Sewer networks collect only a tiny
fraction of city wastewater.
The few wastewater treatment
plants that exist are often
overloaded.

20. This leads to severe water pollution in peri-urban areas

21. Wastewater
Piped water
Also an opportunity?

22. Due to the proximity of markets and lack of
refrigerated transport and storage, a whole
irrigation sub-sector specialized in perishable
exotic vegetables is emerging in and around
growing cities.

23. In the economically important
rural–urban interface, it is difficult
to find a reliable unpolluted water
source.

24. 0
5
10
15
20
25
30
Diluted
wastewater
or polluted
water
Untreated
wastewater
Groundwater Treated
wastewater
River Other
surface
water bodies
Rainfed Irrigation
canal
Open
drainage
Numberofcities
Source: IWMI, RR 127
Global survey of irrigation source in urban and
peri-urban areas:
In and around three of four cities in the developing world,
farmers use polluted irrigation water for the production of high-
value crops

25. Water quality improves over 40 km along the Musi River
Hyderabad
Sources: IWMI/J. Ensink

26. IWMI works closely with WHO and FAO on safe
wastewater reuse
• Assessing the extent of reuse, risks and benefits.
• Developing and testing low-cost options for microbial risk reduction
(multi-barrier approach from farm to fork).
• Supporting international guidelines and capacity building.

27. • health risk mitigation
measures have a RoI
of U$4.9 for each
dollar invested.
Mitigating risks where wastewater
treatment remains a challenge

28. Australia: National target of 30% of wastewater
being recycled by 2015
%
Source: Marsden Jacob Associates 2012

29. Reflections II : Cities as sponges
• Wastewater reuse can minimize risks of urban areas becoming
water sinks and contribute to water needs at basin scale.
• Treatment important: 80% of the contamination of India’s
surface water is due to the lack of treatment facilities.
• Where conventional treatment remains limited, pathogenic
risks can be controlled through safer irrigation practices.
• Reducing nutrient loss is becoming a major environmental
driver of change

30. Urban food demands and waste generation
mirror the same challenges
Source: Wikimedia Commons

31. Source: IWMI
!?
Import/
Export
Livestock
Food
Food crops
and fodder
plants
Soil
nutrients
Organic solid
waste,
sludge &
wastewater
Controlled
and un-
controlled
disposal
Fertilizer
Urban pollution and
nutrient wasting
Peri-urban and rural
nutrient mining
Production
Consumption/
Processing
Cities = vast nutrient sinks
Challenge:
Closing the
nutrient loop

32. Closing the loop is no easy endeavor in the
rural-urban context
Technical solutions for resource
recovery are available, but:
• transport costs are high,
• too dependent on public subsidies,
• projects rarely survive their pilot
periods, and
• big gaps in business thinking.

33. Resource Recovery & Reuse (RRR)
A research flagship of CGIAR-WLE using a business approach to
attract private capital
Old challenges require new thinking

34. New understandings required to close the loop

35. RRR program for water, nutrient and
energy recovery from domestic and agro-industrial waste
 Database of 150+ inspiring RRR business cases
 Selection of 60 cases for in-depth analysis (see map)
 So far 20 promising business models extracted
 Feasibility studies of models starting in 9 cities
 Business model implementation targeting 5 cities

36. Example of a business model currently being implemented
in Ghana as a Public-Private Partnership:
Fecal Sludge Valorization
(returning nutrients and reducing pollution)
Other options combine biogas and nutrient recovery

37. Introducing business models to turn
waste into an asset
• Solid waste and fecal sludge
composting in Asia and Africa
could save billions of US$ per
year, assuming a market for only
25% of the urban organic waste.
• Not a new concept, but many
pilots not viable or sustainable
• Business models for resource
recovery & reuse (RRR) target
private and public investors and
business schools.

38. Some ‘nexus’ implications
Energy reduction in
• Water treatment
• Chemical fertilizer
production and
transport
Environmental benefits
• Reduced pollution of
water bodies
• Reduced nitrogen and
phosphorous demand
• Reduced GHG
emissions

39. Addressing water challenges of rapid urbanization
• Analysis: expand inter-sectoral perspective at basin scale to
include nutrient and carbon emission considerations.
• Peri-urban areas: responsive research, policy and development
focus required to reflect the rapid pace of urban transformation
• Urban management: support to closed loop processes to avoid
cities becoming sinks for valuable resources.
• Agriculture-sanitation interface: exploit new approaches, win-
win solutions and incentive mechanisms.
• Agriculture water productivity: innovations needed to release
freshwater for other sectors needs – who pays?

40. www.iwmi.org/Topics/RRR http://wle.cgiar.org/RRR
Closing the loop