Chapter 6 physical and chemical quality of drinking water
6.2 Physical quality of drinking water
6.2.1 AN OVERVIEW OF PHYSICAL CHARACTERISTICS
The appearance, taste, odour, and ‘feel’ of water determine what people experience when they drink or use water and how they rate its quality; other physical characteristics can suggest whether corrosion and encrustation are likely to be significant problems in pipes or fittings. The measurable characteristics that determine these largely subjective qualities are:
- true colour (the colour that remains after any suspended particles have been removed);
- turbidity (the cloudiness caused by fine suspended matter in the water);
- hardness (the reduced ability to get a lather using soap);
- total dissolved solids (TDS);
- taste and odour;
- dissolved oxygen.
Colour and turbidity influence the appearance of water. Taste can be influenced by temperature, TDS, and pH. The ‘feel’ of water can be affected by pH, temperature, and hardness. Rates of corrosion and encrustation (scale build-up) of pipes and fittings are affected by pH, temperature, hardness, TDS and dissolved oxygen.
Each of the physical characteristics is discussed separately in the fact sheets in Part V. However, there is some overlap with organic compounds, microorganisms and, most notably, the inorganic constituents of water; when this occurs, it is noted and cross-referenced.
6.3 Chemical quality of drinking water
A number of chemicals, both organic and inorganic, including some pesticides, are of concern in drinking water from the health perspective because they are toxic to humans or are suspected of causing cancer.
Some can also affect the aesthetic quality of water.
The presence of chemical in drinking water may result from:
- natural leaching from soils, rocks and mineral deposits into source waters;
- land-use activities in catchments leading to exacerbation of natural processes such as mobilisation of salts;
- run-off from agricultural operations within drinking water catchments;
- biological processes including growth of cyanobacteria and algae in waterways and reservoirs;
- contamination of source water by treated effluent discharge and other point sources within the
- carry-over of small amounts of treatment chemicals;
- addition of chemicals such as chlorine and fluoride;
- corrosion and leaching of pipes and fittings.
6.3.2 ORGANIC COMPOUNDS (REVISED 2011)
Organic compounds are usually present in drinking water in very low concentrations. They may occur either naturally or as a result of human activities. By-products of disinfection are the most commonly found organic contaminants in Australian drinking water supplies. Pesticides and petroleum products are occasionally detected in source water or treated drinking water in Australia, but rarely at concentrations above health-based guideline values.
Physical and Chemical Quality of Drinking Water Chapter 6
Australian Drinking Water Guidelines Version 3.5 81
The by-products of disinfection are the products of reactions between disinfectants, particularly chlorine, and naturally occurring organic material such as humic and fulvic acids, which result from the decay of vegetable and animal matter. Of these disinfection by-products, the trihalomethanes (THMs) are produced in the highest concentrations.
Most disinfectants used to render drinking water safe from pathogenic microorganisms will produce by-products in the disinfection process. Factors affecting the formation of disinfection by-products include:
- the amount of natural organic matter present;
- the disinfectant used;
- the disinfectant dose;
- the time available for reaction (C.t or contact time).
Chlorine is the most common disinfectant; in the chlorination process it reacts with naturally occurring organic matter to produce a complex mixture of by-products, including a wide variety of halogenated compounds (i.e. organic by-products of chlorination). The main by-products are the THMs and chlorinated acetic acids. Many other by-products can be produced, but concentrations are generally very low (usually <0.01 mg/L and often <0.001 mg/L).
Other disinfectants can produce different types of by-products: for example, ozone is known to produce formaldehyde and other aldehydes.
Known disinfection by-products are considered individually in the fact sheets in Part V. It is possible, however, that other disinfection by-products for which no health data are available are present at extremely low concentrations. It is also possible that when these compounds (both known and unknown) are ingested together, their combined effects on health may be different from their individual effects. Epidemiological studies examine disinfection by-products as a generic group, and can be useful in determining overall effects.
A number of epidemiological studies have suggested an association between water chlorination by-products and various cancers (Michaud et al. 2007, Villanueva et al. 2007). This association has been most consistent in relation to cancer of the bladder and rectum, but there are insufficient data to determine concentrations at which chlorination by-products might cause an increased risk to human health.
In experiments with laboratory mice, when concentrates derived from chlorinated drinking water were applied to the skin, there was no increase in the incidence of skin tumours compared with concentrates derived from unchlorinated supplies. Similarly, oral administration of chlorinated humic acids in drinking water did not increase the incidence of tumours compared with animals receiving unchlorinated humic acids, or with saline-treated controls (IARC 1991).
Studies have shown that concentrates of some chlorinated drinking water supplies are mutagenic tosome strains of test bacteria. These effects were consistently found with samples of surface water that had a high content of natural organic compounds at the time of chlorination. A significant proportion of the increased mutagenicity has been attributed to a chlorinated furanone known as MX (Kronberg and Vartiainen 1988).
The International Agency for Research on Cancer has reviewed the available data and concluded that there is inadequate evidence to determine the carcinogenicity of chlorinated drinking water to humans (IARC 1991).