Temperature

(endorsed 1996)

Guideline

No guideline is set due to the impracticality of controlling water temperature.

Drinking water temperatures above 20°C may result in an increase in the number of complaints.

General description

Temperature is primarily an aesthetic criterion for drinking water. Generally, cool water is more palatable than warm or cold water.

In general, consumers will react to a change in water temperature. Complaints are most frequent when the temperature suddenly increases.

The turbidity and colour of filtered water may be indirectly affected by temperature, as low water temperatures tend to decrease the efficiency of water treatment processes by, for instance, affecting floc formation rates and sedimentation efficiency.

Chemical reaction rates increase with temperature, and this can lead to greater corrosion of pipes and fittings in closed systems. Scale formation in hard waters will also be greater at higher temperatures.

Measurement

Temperature measurements should be made with a good quality, mercury-filled Celsius thermometer (APHA Method 2550B 1992).

Typical values in Australian drinking water

Water temperatures in major Australian reticulated supplies range from 10°C to 30°C. In some long, above-ground pipelines, water temperatures up to 45°C may be experienced.

Control in drinking water supplies

Control of water temperature in reticulated supplies is seldom practical or effective. Selective withdrawal from deep reservoirs can be used but this may introduce other water quality problems. Aeration can also be used. In some situations it may be possible to place pipes underground to reduce water temperature fluctuations, or to vary the times water remains in pipes and storage tanks.

Health considerations

The effectiveness of chlorine as a disinfectant is influenced by the temperature of the water being dosed. Generally higher temperatures result in more effective disinfection at a particular chlorine dose, but this may be counterbalanced by a more rapid loss of chlorine to the atmosphere (AWWA 1990).

Chlorine reacts with organic matter in water to produce undesirable chlorinated organic by-products, and higher temperatures increase the rate of these reactions.

Temperature can directly affect the growth and survival of microorganisms. In general the survival time of infectious bacteria and parasites is reduced as the temperature of the contaminated water increases. Naegleria fowleri, which can cause amoebic meningitis, grows between 18°C and 46°C and is likely to occur in nondisinfected water supplies that reach 30°C seasonally. Legionella pneumophila (which causes Legionnaires’ disease) and related bacteria are found in hot and cold water systems, with colonisation occurring in stagnant water at temperatures between 20°C and 45°C. Increased temperatures can also promote the growth of taste- and odour-producing organisms in lakes and impoundments, and in distribution systems.

Guidelines in other countries

The European Economic Community Standards have a guideline value of 12°C and a maximum of 25°C.

The Canadian Guidelines have a recommended value of 15°C.

The 1984 World Health Organization (WHO) Guidelines do not include a value for temperature as control is usually impractical. The 1993 WHO Guidelines require that temperature should be acceptable to avoid consumer complaints.

References

APHA Method 2550B (1992). Temperature: Laboratory and field methods. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

AWWA (American Water Works Association) (1990). Water Quality and Treatment: A handbook of community water supplies. AWWA, 4th edition, McGraw-Hill Inc.