"pH" means the expression of the intensity of the acid or alkaline condition of a solution, such as water, as indicated by the hydrogen ion concentration and expressed as a number on the scale of 0 to 14, with 0 being most acidic, 7 being neutral, and 14 being most basic.
N.H. Admin. Code § Env-Wq 1102.42
(See Revision Note at chapter heading for Env-Wq 1100) #8468, eff 11-1-05