Dissolved oxygen

(endorsed 1996)

Guideline

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.

General description

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).

Typical values in Australian drinking water

In major Australian reticulated supplies the dissolved oxygen concentration is generally greater than 85% saturation. Ground water supplies may have less dissolved oxygen.

Treatment of drinking water

The dissolved oxygen concentration in drinking water can be increased by aeration or ozonation.

Measurement

The dissolved oxygen content of drinking water can be determined on site using an oxygen-sensitive membrane electrode (APHA Method 4500-O Part G 1992). Alternatively, the iodometric method (azide modification) can be used (APHA Method 4500-O Part C 1992).

Health considerations

There have been no direct health effects caused by low oxygen concentrations in drinking water. Indirect effects may result from the corrosion of fittings, which can give rise to higher concentrations of heavy metals such as lead, copper and cadmium, and by the anaerobic generation of hydrogen sulfide and nitrite.

Derivation of guideline

The guideline value of more than 85% saturation is based on aesthetic considerations for taste, odour and prevention of corrosion of pipes and fittings. If the concentration is lower than 85%, an investigation should be carried out to determine the cause.

References

APHA Method 4500-O Part C (1992). Oxygen: Azide modification. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

APHA Method 4500-O Part G (1992). Oxygen: Membrane electrode method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.