mercury, which the indigenous rightly considered a death sentence. Spanish officials also knew the impact on human populations, but did not modify their forced labor policies, since they rightly identified mercury as the key to continued silver production and wealth of the Spanish Empire. The environmental degradation was significant. Deep shaft mining of mercury put miners in direct contact with the element and they were its first victims. However, since the mercury was volatilized in silver ore processing and only partially recaptured, its impact on larger human and animal populations was more widespread since it can be absorbed by breathing. Mercury made its way in to the watershed as well, poisoning water supplies. The toxic impact results in nerve damage, inducing muscle deterioration and mental disorders, infertility, birth defects, asthma, and chronic fatigue, to name just a few. Huancavelica produced approximately 68,000 metric tons of mercury, which went into the air and water of Potosí. Water issues Ethnic conflicts As European populations increased in areas with existing indigenous settlement and agriculture, conflicts over access to water increased. In colonial Puebla, Mexico, European elites increasingly appropriated water indigenous communities needed for their agriculture, with deleterious results to those communities. Urban flooding In general, the presence or absence of sufficient water was a major determinant of where human settlement would occur in the pre-industrial Latin America. Large-scale irrigation projects were not undertaken in the colonial era. However, the major hydraulic project to drain the central lake system in the Basin of Mexico, known as the Desagüe, was undertaken to try to control flooding in the vice-regal capital of Mexico City. Tens of thousands of indigenous men were compelled to work on the project, which diverted their labor from agricultural enterprises. Although the project absorbed massive amounts of forced human labor, it was not until the late nineteenth century when the drainage project was completed. Aqueducts Aqueducts were constructed to supply urban centers with drinking water. Before the Spanish conquest in 1521, the Aztecs had constructed an aqueduct from a spring at Chapultepec (“hill of the grasshopper”) to Tenochitlan to provide freshwater to the urban population of nearly 100,000. It had dual pipes so that maintenance of the aqueduct would not cut off the Aztec capital's water supply. The aqueduct was constructed using wood, carved stone, and compacted soil, with portions made of hollowed logs, allowing canoes to travel underneath. During the Spanish