Fluoridation of drinking water in the Toowoomba water supply

On February 19, 2013 we resolved not to proceed with fluoridation of the regional water schemes, but to continue fluoridating at the Mt Kynoch water treatment plant, which commenced in March 2010. This means that only residents supplied from the Toowoomba water supply scheme will receive fluoridated water.

Who is supplied from the Toowoomba Water Supply Scheme?

The Toowoomba water supply scheme supplies drinking water to all of Toowoomba city, and the localities of Highfields, Cabarlah, Meringandan East, Oakey, Jondaryan, Kingsthorpe, Gowrie Junction, Gowrie Mountain, Meringandan West, Goombungee, Cotswold Hills, Torrington, Glenvale and Westbrook.

Where does the water come from?

The water supplied is a mixture of treated dam water from the Mt Kynoch Water Treatment Plant and bore water supplied by up to 25 bores, although not all bores will be in operation at any one time. The average composition of water supplied across the entire Toowoomba water supply scheme in 2011/12 was 68.5% dam water and 31.5% bore water. These percentages will vary from year to year depending on dam levels, the number of bores available and changes to water quality.

How does this affect the amount of fluoride in the water?

The Mount Kynoch water treatment plant is the only place where fluoride is added to Toowoomba’s water supply. Fluoride is dosed to the target concentration of 0.8 mg/L, plus or minus 0.1 mg/L, as required by the Water Fluoridation Regulation 2008. Toowoomba’s bores do not contain measureable amounts of natural fluoride, meaning that the only fluoride in the drinking water supplied to residents of the Toowoomba water supply scheme is that added at the Mt Kynoch water treatment plant. In practice, this means that the amount of fluoride in the water supplied to a particular area will be directly proportional to the percentage of dam water.

Distribution of Fluoridated water in the Toowoomba Water Supply Scheme

The Toowoomba water supply scheme is very complex, which means that residents of one part of the city will receive water which is different in its proportion of dam and bore water to that received by residents in another part of the city.

The city is made up of a number of distribution zones. Over an extended period of time, each of these zones will receive a relatively consistent mixture of dam and bore water. However, not only will the mixture vary from zone to zone, it will also vary from day to day, depending on the number of bores that are in use at the time, and maintenance works that might require us to temporarily change the source of water for a particular area. It will also vary from property to property within the zone, depending on its proximity to bores, reservoirs and trunk water mains. Because of these variations, it is not possible to accurately predict the mix of surface water and bore water received by any particular property.

Map 1 shows the Toowoomba City Water Distribution Zones and the maximum, minimum and average concentrations of fluoride measured in drinking water supplied to each Toowoomba City zone, as well as to localities outside Toowoomba City. These figures are based on actual measurements on water taken from the sample points marked as red dots on the map. Bore locations are shown as black dots.

FluorideAreasresized

Map 2 divides Toowoomba City into 3 broader areas, those that on average receive 90% or more dam water, those that receive 35% to 89% dam water, and those that receive less than 35% dam water. The equivalent theoretical average fluoride concentrations are 0.7 – 0.9 mg/L, 0.3 – 0.7 mg/L, and less than 0.3 mg/L respectively. The theoretical figures may differ from the actuals recorded due to the inclusion of samples collected when the actual dam water to bore water ratio in various zones differed from the long term average, or when the Mt Kynoch water treatment plant fluoridation facility was not operating.

Again, it must be emphasised that the concentrations shown are long term averages only, and the fluoride concentrations experienced at a particular location and/or time may vary from the zone or area average, but will never exceed 0.9 mg/L. This value is well below the Australian Drinking Water Guidelines health based guideline value of 1.5 mg/L.

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How much fluoride is in my water?

The actual concentration of fluoride in the drinking water at any point is directly proportional to the percentage of dam water supplied to that point. An area that receives 100% dam water will receive, on average, 100% of the regulated fluoride dose, which is 0.8 mg/L. At no time will the fluoride concentration in any water supplied to residents of the Toowoomba drinking water scheme exceed 0.9 mg/L, that is 0.8 mg/L + 0.1 mg/L. On average, areas that receive a lower proportion of dam water will receive a proportionally lower fluoride concentration.

 

Queensland Department of Health dental experts have advised that while 0.8 mg/L is considered to be the optimum drinking water fluoride concentration for our region, doses of 0.4mg/L or greater will have a beneficial effect.

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