The chemical reaction is alkaline, turning red litmus paper blue.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
Did you test the distilled water with litmus paper?
"Lessons on Soil"
E. J. Russell
Dip into it the end of a piece of blue litmus paper, and record the result.
"An Introduction to Chemical Science"
R.P. Williams