PH (eng)
- Slovak term: Slovenský termín
- The pH of a solution is the negative common logarithm of the hydrogen ion activity:
pH = −log (H+) (WHO 2007) - An expression of the intensity of the basic or acid condition of a liquid (WHO 2006).
Explanation
Most substances have a pH in the range 0 to 14, although extremely acidic or extremely basic substances may have pH less than 0 or greater than 14. The pH of water is a measure of the acid-base equilibrium and, in most natural waters, is controlled by the carbon dioxide-bicarbonate-carbonate equilibrium system (WHO 2007). An increased carbon dioxide concentration will therefore lower pH, whereas a decrease will cause it to rise. Temperature will also affect the equilibria and the pH. In pure water, a decrease in pH of about 0.45 occurs as the temperature is raised by 25°C. In water with a buffering capacity imparted by bicarbonate, carbonate and hydroxyl ions, this temperature effect is modified. The pH of most raw water lies within the range 6.5-8.5. pH is an important consideration in the management/controlling of disinfection by-product formation arising from treatment processes (Amy et al. 1987 and Stevens et al. 1976).
Example
Although pH usually has no direct impact on water consumers, it is one of the most important operational water quality parameters. Careful attention to pH control is necessary at all stages of water treatment to ensure satisfactory water clarification and disinfection. For effective disinfection with chlorine, the pH should preferably be less than 8.0. The pH of the water entering the distribution system must be controlled to minimize the corrosion of water mains and pipes in household water systems. Failure to do so can result in the contamination of drinking-water and in adverse effects on its taste, odour and appearance.
References
- Amy, G.L., Chadik, P.A., and Chowdhury, Z.K. (1987) Developing models for predicting trihalomethane formation potential and kinetics. J. Am. Water Works Assoc., 79: 89.
- Stevens, A.A., Slocum, C.J., Seeger, D.R., and Robeck, G.G. (1976) Chlorination of organics in drinking water. J. Am. Water Works Assoc., 68: 615.
- WHO (2007) pH in Drinking-water: Revised background document for development of WHO Guidelines for Drinking-water Quality.
- WHO (2006) Guidelines for the safe use of wastewater, excreta and greywater
