Source Source: P. Piriou, E.D. Mackey, I.H. Suffet and A. Bruchet (2004) Water Science Technology, Vol 49 No 9 pp 321-328.

This paper examines the characterisation of consumer perception and acceptance to chlorinous tastes in drinking water. This study was carried out as part of the AwwaRF (American Water Works Association Research Foundation) project "Public Perception of Tap Water Chlorinous flavor" (#2639). Extensive taste testing by trained and untrained panellists was performed to investigate public perception of chlorinous tastes.

The paper explains that chlorinous flavour (taste and odour) is a leading cause of customer complaints and dissatisfaction with drinking water. Consumers often associate taste & odour with safety. Disinfectants such as chlorine are essential in maintaining water quality during transport to the customer tap. Therefore, in order to determine what level of disinfectant is acceptable, water suppliers need to characterise customer perception and acceptance to chlorinous flavour.

A group of trained panelists (4 to 5 experts) and two groups of untrained panelists (10 average consumers from the US, and 10 from France) determined flavour threshold concentrations for samples of chlorine, monochloramine and chlorine dioxide primary disinfectants. The trained panelists used two methods: The Flavor Profile Analysis (FPA) protocol, which requires a description of the flavours present in the sample; and the Forced-Choice Triangle test, which only defines the difference between samples. The untrained panels used the Forced-Choice Triangle test only.

Trained panelists found thresholds of around 0.05 mg/L for chlorine, 0.10 mg/L for monochloramine and 0.2 mg/L for chlorine dioxide. Compared to the untrained panelists, trained panellists were 2 to 4 times more sensitive to chlorine and monochloramine. However both trained and untrained panels found similar thresholds for chlorine dioxide.

Compared to the French untrained panel, the US untrained panel was 5 times less sensitive for chlorine and 10 times for monochloramines. This result may be linked to each country's chlorination residual practice; France uses a low residual in the drinking water distribution system (in the order of 0.1 mg/L) while many utilities in the US rely on a comparatively high residual (in the order of 1 mg/L).

This study also investigated water quality characteristics that may influence chlorine taste perception. These included water temperature (15-25°C), total dissolved solids (TDS) and background tastes (earthy-musty taste). Among the water quality characteristics investigated that may influence chlorine perception, temperature had no significant influence on chlorine perception, whilst the influence of TDS was unclear. However, the increase of the earthy-musty background taste induced an antagonistic shift of the perception of chlorine flavour, leading to the increase of chlorine flavour threshold.

This study showed that public perception may be influenced by the chlorination practices of the country they live in, and the presence of any earthy-musty background tastes in the drinking water. Also, trained panellists may significantly overestimate the average consumer's ability to perceive chlorine.

Sydney Water Response:

Sydney Water uses chlorine and monochloramine to disinfect drinking water to kill micro-organisms that could cause disease. The Australian Drinking Water Guidelines lists the odour threshold as 0.6 mg/L for chlorine and 0.5 mg/L for monochloramine. Disinfectant level in Sydney's tap water varies from around 0.2 mg/L to 1.5 mg/L.. Sydney Water carries out an annual Residential Customer Survey to study its consumers view on its products and service. Consumers views on the taste and odour of water are sought as part of this survey. Data collected is analysed and, opportunities for improvement identified and actions taken where necessary. Sydney Water has a Taste & Odour panel comprising specially trained scientists. This panel conducts both routine and special events taste & odour testing to assist Sydney Water in making decisions related to the provision of safe drinking water that meets the requirements of the Australian Drinking Water Guidelines.