Since 1994, the Lerma river also receives residual
water from the water treatment plant EPCCA
and from two other similar water-treatment plants
from Toluca city with a maximum treatment capacity
of 26.3 m3rs. The average annual water
flux to the Alzate Reservoir is 5.2 m3rs, although
during the raining season in July it can increase
up to 10 m3rs Barcel´o-Quintal et al., 1996..
According to INEGI 1994., the Lerma river receives
1.3 m3rs of waste water discharges from
the industry situated on the Toluca]Lerma area
and 4 m3rs of waster water from domestic activities.
Until now a natural oxidation process is
taking place in the Alzate Reservoir decomposing
organic material and making the contamination
process less severe in the reservoir. However, the
combination of the wastewater discharges, the
over-exploitation of the aquifer, and the decrease
of the runoff water volume that occurs during dry
weather, has deteriorated up to a warning level,
the self-cleaning capacity of the water body, producing
a change in the water cycle and a near
imbalance of the ecosystem.