pH is a measure of the hydrogen ion activity. It is strictly defined as the negative common logrithm of the hydrogen ion activity. It is interpreted to mean the "acidity" or "base" nature of a solution.
In most waters the acid-base realtionship is controlled by the chemical equilibria of the carbon dioxide - bicarbonate - carbonate ions. Factors such as temperature effect this system.
pH alteration occurs during treatment processes but should always remain within the range of 6.5 - 8.5 afterwards.
No direct relationship. Changes in pH can effect the toxicity of some compounds e.g., ammonia.
Colour is a physical characteristic of water. Some boreholes produce ferruginous waters but the majority of borehole sources will be clear and bright in appearance.
Conductivity is a measure of a the electric current carried in the water by ionized substances. Water's with a high mineral content tend to have higher conductivities.
Conductivity is useful as an early warning of possible ingress into the supply and distribution system.
Values often differ between source waters and can be a guide to blending proportions between them in distribution.
None directly, however the ionic charateristsics of the particles which make up the value may do on an individual basis.
- see turbidity
This determinand should always be considered with turbidity. It gives a more precise measurement for non homogeneous mixtures of contaminants, e.g, algal breakthrough at a works.
The rates of chemical reactions generally increase with increasing temperature. The concentrations of reactants and products in chemical equilibria can also change with temperature. At the normal range of temperatures encountered in works and distribution systems microorganisms which proliferate will generally be favoured by higher temperatures. Formation of some undesirable chlorination by products is favoured by higher temperatures e.g., Trihalomethanes.
Temperature can therefore affect every aspect of water supply and distribution and is of fundamental importance.
None directly.
This is a quick and easy measure of the suspended matter in water such as clay, silt, colloidal particles and microbiota. It is more practical that suspended solids for most purposes. It is used as an online monitor on water quality. Currently the nephelometric method is used for the measurement of turbidity. Nephlometeric turbidimeters measure the intensity of light scattered at 90 degrees to the path of the incident light. This measurement is expressed in NTU (nephelometric turbidity units).
The microbiological quality of the water can be affected by turbidity. Suspended particles may shelter microorganisms from disinfection or adsorb nutrients onto their surfaces which can sustain these organisms. This is of particular concern when ultra violet light is used as a disinfecting agent as the light may not be able to kill them.
Although no health effects are directly related to turbidity which is a physical property of the water it is indirectly related to many potential ones e.g., aesthetic, corrosion, protection of pathogenic microorganisms from disinfection processes, provision of nutrients for pathogenic microorganisms and increase chlorine demand. The WHO recommend a operational maximum of 1 NTU at the final tap of a treatment works with a guideline value of 5 being objectionable to customers.
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