pH
"A measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions." (U.S. Geological Survey, 2019)
Sources
U.S. Geological Survey (USGS). "Water Science Glossary Terms". USGS Water Science School. (2019). Link: https://water.usgs.gov/edu/dictionary.html#W