A lot of nouns for liquids as well as a lot of abstract things are in the ma- class and only ever with ma-

maji = water
matope = mud
mafuta = oil, fat
maziwa = milk (also "lakes" or "breasts")
mabadiliko = change(s)
mazungumzo = conversation(s)
mapokezi = reception

I don't think waziwa means anything at all.