Smallholder dairy farmers from the State of Mexico, México face the challenge of meeting the quality standards established by
Mexican regulations stated in the Mexican Norm (NMX) NMX-F-700-COFOCALEC-2004 for raw milk. The objective of this work
was to determine the physicochemical quality of raw milk in different seasons, regions and among farmers whose principle or
complimentary income proceeds from the dairy activity. Adulteration of milk by added water was also evaluated. The variables
measured were pH, acidity, density, fat, protein, lactose, total solids, ash content and added water. Three hundred and sixty
samples were taken during six experimental periods, from August 2003 to July 2004. A split plot design was used, where the
blocking factor were: the zones, the main plot, the farmers according to their dairy activity and the split plots, during the six
sampling periods. Results were analyzed by analysis of variance, Tukey test, correlation and regression analysis. It was observed
that the physicochemical quality of the milk meets the levels established by the NMX for north and south regions of Mexico, for
importance and periods. Signifi cant differences (P < 0.05) were observed for fat, density and total solids contents between zones.
Signifi cant differences (P < 0.05) were found for density between type of farmers, and between periods (P < 0.05) for fat, density
and ash contents. It was observed that 6.4% of samples were adulterated with added water, which produced a negative correlation
between the percentage of added water and milk density (r = 0.9, P < 0.05), protein and fat contents (r = 0.9, P < 0.0).