I live in Xalapa and am shopping for an inexpensive water filter that will do the job. I find one at Home Depot that looks alright, and I'm trying to get information on the type and its capabilities. However, there seems to be something lost in translation. "Purificador sobre tarja"? I don't find anything about "card purifiers" in English. What does "tarja" mean? Could it possibly mean "cartridge"?
Tarja (from French targe, "round shield") means "sink", that is, the bowl usually found in the kitchen in a house, together with the counter where it is installed and its water taps. Curiously this meaning can't be found in the DLE. In the DAMER (Diccionario de Americanismos) the entry for tarja says it's a memorial plaque. This might or might not have something to do with its use in Mexico, if the plaque is a reference to the counter or else the round, concave shape of a shield can point to the shape of the sink. I don't know if tarja means "sink" elsewhere. In Spanish this is known more commonly as fregadero (and in Argentina and Paraguay it's bacha).
A water purifier can come prepared for installation as an appliance above the counter (sobre tarja) or hidden behind it (bajo tarja). (Pic from here.)
It seems the usual terms in English for these are "under-sink" and "over countertop".