Middlemount (Queensland) – Dissolved Oxygen
2016/17: Middlemount (Queensland) Dissolved Oxygen 99% (max), av. 91.93%. 1 exceedence during year.
2015/16: Middlemount (Queensland) Dissolved Oxygen 96% (max), av. 88.967%. 2 exceedences during year.
Based on aesthetic considerations, it is desirable that the dissolved oxygen concentration in drinking water be greater than 85% saturation.
No health-based guideline value has been set for dissolved oxygen.
Drinking water will generally contain an adequate concentration of dissolved oxygen; however, under some circumstances the oxygen concentration may be reduced. This may occur, for instance, where water has been drawn from deep storages, where there is considerable growth of microorganisms in a distribution system, or following prolonged periods of high water temperature.
Low oxygen concentrations or anoxic conditions enable nuisance anaerobic microorganisms to grow, producing by-products that affect the aesthetic quality of the water and increase corrosion of pipes and fittings.
There are a number of such nuisance microorganisms. Manganese-reducing bacteria produce black manganese deposits which can slough off pipes and soil laundry. Sulfate-reducing bacteria can produce hydrogen sulfide, giving drinking water a ‘rotten egg’ smell. Nitrate-reducing bacteria can produce nitrite. Iron-reducing bacteria can increase the concentration of ferrous ion in solution which will lead to the deposition of insoluble ferric salts when aeration is increased.
Localised pH changes associated with the growth of nuisance microorganisms can cause rapid corrosion in metal pipes.
Water from groundwater sources will generally have low oxygen concentrations and while this may cause no difficulties for most supplies, some supplies may need aeration to improve water quality (e.g. taste and odour). ADWG 2011
Based on health considerations, the guideline value for total chlorine in drinking water is 5 mg/L.
Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion. Chlorine and hypochlorites are toxic to microorganisms and are used extensively as disinfectants for drinking water supplies. Chlorine is also used to disinfect sewage and wastewater, swimming pool water, in-plant supplies, and industrial cooling water.
Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. Water authorities may need to exceed the odour threshold value of 0.6 mg/L in order to maintain an effective disinfectant residual.
In the food industry, chlorine and hypochlorites are used for general sanitation and for odour control. Large amounts of chlorine are used in the production of industrial and domestic disinfectants and bleaches, and it is used in the synthesis of a large range of chemical compounds.
Free chlorine reacts with ammonia and certain nitrogen compounds to form combined chlorine. With ammonia, chlorine forms chloramines (monochloramine, dichloramine and nitrogen trichloride or trichloramine) (APHA 2012). Chloramines are used for disinfection but are weaker oxidising agents than free chlorine.
Free chlorine and combined chlorine may be present simultaneously (APHA 2012). The term totalchlorine refers to the sum of free chlorine and combined chlorine present in a sample.
Chlorine (Free) ADWG Guideline: 5mg/L (Chlorine in chloraminated supplies 4.1mg/L). Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion.
Chlorine (Total) ADWG Guideline 5mg/L (chloraminated supplies 4.1mg/L): The term total chlorine refers to the sum of free chlorine and combined chlorine present in a sample
Middlemount (Queensland) – Manganese
2014/15: Middlemount (Queensland) – Manganese 4.5mg/L (maximum)
Manganese: ADWG Guidelines 0.5mg/L. ADWG Aesthetic Guideline 0.1mg/L
Manganese is found in the natural environment. Manganese in drinking water above 0.1mg/L can give water an unpleasant taste and stain plumbing fixtures and laundry.