A hand held ion tester includes a housing sufficiently small to be conveniently held in a human hand. A sample chamber is formed in the housing and has a sample inlet in the upper surface of the housing. An ion selective electrode is positioned in the sample chamber so as to be in liquid communication with samples positioned in the sample chamber. A key board and a display are positioned on the upper surface of the housing and a central processing unit contained within the housing is electrically coupled to the ion selective electrode, the key board and the display. The central processing unit is designed and connected to receive signals from the ion selective electrode, process the signals and display processed information on the display.