Water management in Greater Mexico City

Overcoming these challenges is complicated by fragmented responsibilities for water management in Greater Mexico City: Given the size and political importance of Greater Mexico City, a major flood or a major water supply interruption would be a national political crisis potentially threatening the stability of the federal government.

[2] Besides these well fields, the bulk water supply infrastructure of Greater Mexico city consists of two systems: Lerma and Cutzamala.

[2] The three interceptors are: The total dry weather flow for Greater Mexico City, which consists mainly of untreated municipal wastewater, was estimated at 44 m3/s in 1993.

Because of this rainfall pattern, the general drainage system was designed to carry 200 m3/s over a 45-hour period [2] Until 1910 the Grand Canal functioned purely by gravity, with an inclination of 19 cm per km.

It consists of a deep tunnel, the Emisor Central with a length of 68 km and a depth of up to 250 m. It today constitutes by far the most important element of the Mexico City drainage system.

The wastewater, whether raw, partially treated or mixed with rainfall, is highly valued by the farmers because of its ability to improve soil quality and because of its nutrient load that allows increased productivity.

However, the wastewater is contaminated with pathogenic organisms and toxic chemicals that constitute a health risk for both farmers and consumers of agricultural products.

A major wastewater reclamation and reuse scheme exists at Lake Texcoco in conjunction with programs for flood control and dust abatement.

The reuse component of the Texcoco plans include the construction of a facultative lagoon wastewater treatment system, and reclamation of the collected storm water for agricultural irrigation.

In a separate program carried out by the Federal District, a pilot plant injected advanced treated water directly into the aquifer at a rate of up to 0.05 m3/s.

Land subsidence has been caused by groundwater overexploitation during the last hundred years, and has been up to 9 meters, resulting in damages to buildings, streets, sidewalks, sewers, storm water drains and other infrastructure.

[6] The Mexico Valley Basin has faced droughts, recurrent floods and other hydrological and climate-related hazards since pre-Hispanic and colonial times.

[17] The hydrological cycle used to be in equilibrium; elevated mixed forests interacted with infiltration, evapotranspiration, and with the system of rivers, seasonal streams and lakes that acted as watersheds, or drainage basins, for precipitation runoff.

[18] Additionally, the high speed at which abundant surface runoff runs down the valley's slopes poses a big risk for nearby populations.

[19] Most of the floods in the Valley can be explained due to the difference in altitude and the inability of the sewerage system to pump the water out during the monsoon season.

[18] The Great Canal has lost its gradient due to land subsidence in some parts of the city, losing its discharge capacity from 90 m³/second to 12 m³/second in the last 30 years, and the secondary sewerage network is insufficient to carry high volumes of stormwater and wastewater.

[18] Poor neighborhoods located in hillsides are particularly affected[20] by waterborne, diseases, suspension of electricity service and need for piped water supply.

[17] In low-lying neighborhoods such as Iztapalapa, residents are so accustomed to seeing a fetid sea of sewage rise in the streets that they have built miniature dikes in front of their homes.

The Groundwater under Mexico City thus is believed to be increasingly vulnerable to contaminants from waste dumps and industrial sites leaching to the aquifer.

When the soil is permeated by sewage from leaking sewers or from other sources, then leaky pipelines will be infiltrated with contaminated water when pressure is low.

The standard levels of chlorine (0.2 milligrams/liters) maintained in the distribution system as it reaches the customer's tap are not sufficient to inactivate microorganisms that may have entered the pipelines.

According to a study by the International Water Management Institute (IWMI), these risks need to be carefully considered, but the importance of this practice for the livelihoods of countless smallholders must also be taken into account.

There is a major gap between the cost of supplying water, a quarter of which is imported through expensive interbasin transfers from the Lerma and Balsas basins, and what is recovered from users.

In early August 2009, the head of Conagua, José Luis Luege, had announced an "imminent and indefinite increase in water rationing in the Valley of Mexico and federal district.

[36] Out of the discharge of the Emisor Oriental 23 m3/s would be treated in a planned wastewater treatment plant in El Salto in Hidalgo State to deliver water to the Tula Irrigation District.

The Plan is expected to relieve pressure on the aquifer by 6.8 m3/s, including 3.3 m3/s by reducing leakage, 1 m3/s through water conservation and 2.5 m3/s by recharging groundwater with treated wastewater.

Manuel Camacho Solís, the Head of Government of the Federal District from 1988 to 1997 who was appointed by President Carlos Salinas (PRI), led the process of private sector participation in water supply in Mexico City in the early 1990s.

[45] In November 1992 bids were launched, in March 1993 the results were announced and in November 10-year service contracts were signed with four firms, each for one block of the capital: The process of private sector participation foresaw three phases: The city remained in charge of the water production, treatment and main distribution infrastructure, as well as some aspects of collection and the sanitation infrastructure.

Collection efficiency actually declined from 84% to 69%[45] The service itself remained unchanged in terms of intermittency of supply and water quality, since these aspects were not part of the contracts.

The IDB project, which closed in 2005, foresaw the construction of 4 wastewater treatment plants with a total capacity of 74.5 m3/s as well as the rehabilitation of drainage systems.