Mexico: Water quality and dams on the rise in Mexico

Mexico’s national water commission (Conagua) has released its water quality data for 2023 revealing that while 55 per cent of groundwater sites were compliant with regulations, only 27 per cent of monitored surface water sites were found to be compliant.

Surface water quality

Conagua operated 450 sites in its surface water monitoring network during 2023.

Water quality was analysed for eight ‘indicator’ parameters: Five-day biochemical oxygen demand (BOD); chemical oxygen demand (COD); total suspended solids; fecal coliforms, escherichia coli (e-coli); fecal enterococci, percentage of dissolved oxygen saturation; and acute toxicity.

Each site rated using a traffic light system based on compliance with the indicator parameters: Green (excellent, when there is compliance with all parameters); yellow (when compliance is not met for one or more parameters); and red (where there is no compliance for BOD, COD, e-coli, or fecal enterococci).

Using this system, of the 450 monitored surface water sites, 27.3 per cent were rated green, while 21.8 per cent were rated yellow and 50.9 per cent were rated red.

Looking at the indicators individually, the percentages for sites rated green were: 80 per cent rated green for fecal enterococci; 63.5 percent for dissolved oxygen saturation; 44.6 per cent for total suspended solids; 27 per cent for BOD; 17.2 per cent for fecal coliforms; 10.7 per cent for e-coli; and 1.4 per cent for COD. 60.9 per cent presented no toxic acuity.

Groundwater quality 

Conagua monitored 606 groundwater sites during 2023, with the quality of water intended for drinking, consumption or agricultural irrigation analysed against 14 physicochemical and microbiological indicator parameters: Fluorides; fecal coliforms; nitrate nitrogen (N_NO₃); total arsenic; total cadmium; total chromium; total mercury; total lead; alkalinity; electrical conductivity; total hardness; total dissolved solids; total Iron; total manganese.

A traffic light system is also used to indicate compliance: Green shows compliance with all 14 parameters. Yellow shows that one or more of the following parameters was not met: Total alkalinity; electrical conductivity; total hardness; total dissolved solids; total iron; and total manganese. Red, however, indicates that one or more of the following parameters were not met: Fluorides; fecal coliforms; nitrate nitrogen; total arsenic; total cadmium; total chromium; total mercury; total lead.

In 2023, 55.4 per cent of the 606 sites were rated green, 12.9 per cent were rated yellow; and 31.7 per cent were rated red.

Dams refilling and floods during rainy season

Seasonal rains have brought their own challenges to Mexico. A country that has been ravaged by long-term drought and water scarcity concerns has received heavy rainfall in parts, causing floods. The period from Jun 29 to July 28 saw over 16 centimetres of rainfall, representing am average 30 per cent increase on the same period according to records dating 1991-2020.

As a result, Conagua announced that the area of country suffering from moderate to exceptional drought decreased from almost 74 per cent to just over 51 per cent from July 1 to 15. It also announced that levels within the country’s 210 main dams increased from 42 per cent to 46 per cent in the period July 15 to July 29.