What is pH and what is its significance in water treatment?

pH is a measure of hydrogen ion concentration indicating acidity or alkalinity of water on a scale of 0-14 (7 is neutral). In water treatment, pH affects coagulation efficiency (optimal at 6-8 for alum), disinfection effectiveness (chlorine more effective at lower pH), corrosion control, and biological treatment processes. Drinking water should have pH between 6.5-8.5. pH adjustment uses lime, soda ash, or acids.