ahuatl.

This is seen as a surname in Cholula in 1867. One Tomás Ahuatl reported the death of his son, Severo Ahuatl, five years old. This family pertained to San Gregorio Zacapechpan, part of the municipality of Cholula. The cronista of Cholula, Manuel Tlatoa Guízar, does not cite his source for this death announcement, but it may be an old newspaper. He reports that, in Santa María Zacatepec, the name "Ahuatl" was Hispanized to "Agua," especially in the plural ("por decir los Ahuatls decía los Aguas") even though the name does not mean water.
Manuel Tlatoa Guízar, "Tlacamecayotl," unpublished document, shared with Stephanie Wood in 2015. One thing that is not clear is whether the surname Agua referred to ahuatl (as in oak tree) or ahhuatl (as in long thorn or hairy worm).