Bacteriological and Physico-chemical Study of Household Water in Mexico City

Water in Mexico City is supplied mainly by wells, followed by the Cutzamala System, the Magdalena River and natural springs. Mexico's geological framework consists of various types of rock which confer different qualities to the water circulating around them. The quality of water for human consumption must be assessed regularly since it is constantly changing as a result of both natural and anthropogenic pollutants. The aim of this study therefore was to determine the water quality of Mexico City households. Eleven delegations were sampled, choosing three households in each. Different sites were sampled in each house, including the main stop valve, water tanks and/or cisterns, kitchen and bathroom faucets and 20-liter carboys. The bacteriological parameters determined were total coliforms, fecal coliforms and 18 physico-chemical parameters. Of the 33 houses sampled, 16 presented no contamination of total or fecal coliforms in the main stop valve or interior. Fifteen had bacterial contamination in the interior and 10 were only contaminated in the main stop valve, which was related to little or no chlorination. Of the 19 carboys analyzed, 11 had bacterial contamination. Physico-chemically, only some houses were outside the norm in one or more of the following parameters: ammoniacal nitrogen, nitrates, dissolved solid turbidity and residual free chlorine. All, however, exceeded the limit for manganese. Delegation 4 presented the greatest differences in relation to salt content, while delegation 2 had the most similitude. In conclusion, the delegations whose three houses had no bacteriological contamination in neither the main stop valve nor the interior and which also gave the best physico-chemical results were 8 and 11; the worst delegations with all three houses contaminated in main stop valve and/or interior were 2 and 4. Regular cleaning and care of interior water deposits is highly important to avoid internal contamination.