What does pH measure in water?

pH measures the hydrogen ion concentration in water, which is crucial for understanding the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14, where a pH of 7 is considered neutral, values below 7 indicate acidic conditions (higher hydrogen ion concentration), and values above 7 indicate basic or alkaline conditions (lower hydrogen ion concentration). Monitoring pH is vital in water treatment processes because it affects chemical reactions, microbial activity, and the solubility of metals and other substances within the water. Proper pH levels are essential to ensure water quality and effectiveness in disinfection processes.

The other choices do not directly relate to the measurement of pH: conductivity pertains to the water's ability to conduct electricity due to dissolved ions, hardness refers to the concentration of calcium and magnesium ions, and temperature measures how hot or cold the water is. Each of these factors plays a role in water quality, but they do not indicate the acidity or alkalinity of the water as pH does.