The Planned and Unplanned Reuse of
Mexico City's Wastewater
Author: Blanca Jiménez-Cisneros, PhD (Universidad Nacional Autónoma de México)
Mexico-Mexico City
Project Background or Rationale
Mexico City is located in what used to be a closed
basin, at an altitude of 7,350 feet (2,240 meters above
sea level). The basin was artificially opened in 1857 to
dispose of waste and stormwater. Mexico City is the
capital of Mexico and comprises the Federal District
plus 37 municipalities, and is home to 21.4 million
people. Water availability in the basin is of the order
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43,600 gallons/inhabitant/yr (165 m /inhabitant/ yr) and
there is a water intensity use of 120 percent. Total
demand for water is around 1,950 mgd (85,700 L/s).
The local aquifer is overexploited by 120 percent
(CONAGUA, 2010), leading to the subsidence of the
soil in some places at a rate of up to 18 in/yr (40
cm/yr). In addition, water has to be imported from two
other basins. One is located 62 mi (100 km) away,
from which water is gravitationally transported, while
the other is 81 mi (130 km) away, and water must
pumped up a height of 3,600 ft (1,100 m). Despite
these efforts, one million people in the city depend on
the delivery of a limited amount of water in tankers,
while the rest of the population receives water through
the network intermittently and sometimes at a very
reduced flow, rendering it necessary to have water
storage tanks and pumping systems in the home
(Jiménez, 2008).
To face the challenge of meeting a constantly
increasing demand for water, the local water utilities
which also manage wastewater have implemented
different projects to reuse wastewater for municipal
and industrial purposes, some of which have been in
operation since 1956. In addition, the Federal
Government has been responsible for a program of
reuse of water in Mexico City and a second basin for
agricultural irrigation since 1920 (Jiménez, 2010).
Capacity and Type of Reuse
Application
At the present time, 6 mgd (260 L/s) of water are
reused to supply different industries. It is problematic
to sell treated wastewater to industry as it is more
2012 Guidelines for Water Reuse
expensive than tap water and there are no compulsory
rules to oblige companies to use reclaimed water. It is
estimated that with a proper legal framework industrial
reuse could be increased by an additional 23 mgd
(1,000 L/s). Furthermore, 30 mgd (1,300 L/s) of water
is supplied to power plants merely for cooling. Nearly
46 mgd (2,000 L/s) are used for irrigation of green
areas, recharge of recreational lakes and agriculture;
27 mgd (1,200 L/s) are used for groundwater recharge
and 4 mgd (175 L/s) for car washing. New car washing
service centers are compelled to use reclaimed water.
In addition, one treatment plant produces 14 mgd (600
L/s) for ecological purposes. Its effluent is being used
to recharge a lake that was dried by the Spanish
during the colonial period and was the source of
particulate matter heavily polluting Mexico City’s air.
The last planned public projects began to operate at
the end of the 1980s. In most of these cases, e.g. the
power plant, the restored lake, some irrigated areas
and recreational lakes, pipelines convey treated water
to the facilities. The other projects receive effluent from
water tankers. The amount of water reused from public
plants represents 10 percent of the total supply.
Additionally, although they are not formally registered,
several dozen private wastewater treatment plants in
sports clubs, golf courses and schools treat
wastewater and reuse it for lawn irrigation or toilet
flushing. Private reuse is not controlled by the
government.
The remainder of the wastewater produced in Mexico
City, amounting 1,370 mgd (60,000 L/s), is reused with
no treatment for the irrigation of 220,000 acres (90,000
hectares) in the Tula Valley (Figure 1). This is located
62 mi (100 km) north of Mexico City. Reuse has been
performed, although not always officially, for more than
110 years and as a result the infiltration of the water
used for irrigation (estimated in more than 570 mgd
(25,000 L/s) has created new groundwater sources.
These sources are used to supply the 500,000 people
living in the Valley with municipal water, using only
chlorination for treatment. The water has proven to be
of acceptable quality (Jiménez and Chavez, 2004)
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Appendix E | International Case Studies
Figure 1
Use of water in Mexico City and the Tula Valley
thanks to several natural occurring treatment
mechanisms that happen during its transport, storage,
and infiltration into the soil. In fact, some pollutants
such as heavy metals and emerging pollutants have
been shown to remain in agricultural soils for several
years or even decades (Siebe, 1995; Gibson et al.,
2007; Duran et al., 2009).
For public reuse, water standard NOM-003SEMARNAT-1997 is in use, but this only covers
restrictions for biological pollutants. To regulate the
infiltration of reused water to groundwater, a relatively
new standard (NOM-014-CONAGUA-2003) has been
adopted. This basically only requires compliance with
the Mexican drinking water standard prior to infiltration.
Water Quality Standards and
Treatment Technology
The planned reuse of wastewater for industrial and
municipal purposes is always performed after at least
secondary treatment coupled with filtration. The
effluent produced has proven to be adequate for most
uses, other than for the recharge of recreational lakes,
notably the Xochimilco Lake, which is currently
suffering from eutrophication. The power plant
provides tertiary treatment to a secondary effluent at
its own cost to avoid the formation of deposits in its
cooling towers. To recharge the aquifer, treatment up
to the tertiary level is provided, to remove suspended
solids and organic matter. No data has been published
with regard to effluent quality or its impacts on
groundwater.
With regard to standards, the reuse of wastewater for
agriculture has been regulated since the 1980s using
criteria that were modified in 1986 (NOM-001SEMARNAT 1986) to manage the quality of the
treated water to control health risks, i.e., by limiting the
fecal coliform content to 103 MPN/100 mL and 1
helminth egg/L for non-restricted irrigation or 5
helminth eggs/L for restricted irrigation. In addition, a
higher content of BOD was allowed in order to improve
the quality of agricultural soils while the amount of
heavy metals was limited using values set out by the
EPA, 2004 Guidelines for Water Reuse. There is no
standard for the reuse of water for industrial purposes.
2012 Guidelines for Water Reuse
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Appendix E | International Case Studies
The massive reuse of wastewater for agricultural
irrigation in the valley is performed with no treatment at
all, although plans to treat the wastewater and its
financing have been in place since the mid 1990s.
Project Funding and Management
Practices
All investments for public projects have been through
public funding. All but two wastewater treatment plants
providing water to industries have been operated by
private companies since the mid 2000s. Public reuse
projects are managed by the water utilities of Mexico
City and the municipalities, while the reuse of water on
agricultural fields outside the Mexico City basin is
operated by the federal government.
Institutional/Cultural Considerations
In general, society is aware of the reuse of water and
considers it a positive practice. In fact, in the city there
are many examples of people, forced by the lack of
water, reusing wastewater from showers, or the
washing of clothes for lawn irrigation or the manual
flushing of toilets with graywater.
Successes and Lessons Learned
The main lessons learned are that relatively low risk
practices for reuse have been readily accepted by a
society that suffers from lack of water. However,
possible future reuse projects, either in the form of
new sources of water from the Tula Valley or the direct
reuse of wastewater in Mexico City for drinking
purposes, probably will not be accepted as easily for
many reasons. Perhaps it is time for Mexico City to
begin to plan to control, its urban growth.
2012 Guidelines for Water Reuse
References
CONAGUA 2010 Water Statistics, SEMARNAT [In Spanish].
Jiménez, B. and Chávez, A. 2004. Quality assessment of an
aquifer recharged with wastewater for its potential use as
drinking source: “El Mezquital Valley” case. Water Science
and Technology, 50(2): 269–273.
Jiménez, B. (2008) Water and Wastewater Management in
Mexico City in Integrated Urban Water Management in Arid
and Semi-arid Regions around the world. L. Mays Editor.
Taylor Francis Ltd.
Durán-Álvarez, J.C., Becerril E., Castro V., Jiménez B., and
Gibson R. (2009) The analysis of a group of acidic
pharmaceuticals, carbamazepine, and potential endocrine
disrupting compounds wastewater irrigated soils by gas
chromatography-mass spectrometry. Talanta 78(3):1159-66.
Gibson, R., Becerril, E., Silva,V. and Jiménez B. (2007)
Determination of acidic pharmaceuticals and potential
endocrine disrupting compounds in wastewaters and spring
waters by selective elution and analysis by gas
chromatography – mass spectrometry. Journal of
Chromatography A, 1169(1-2):31-39.
Siebe, C. Heavy metal availability to plants in soils irrigated
with wastewater from Mexico City, Water Science and
Technology, 1995; 32 (12):29-34
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