Tag Archives: NZ Water

Water treatment chemicals – why pick on fluoride?

Almost every person arguing against fluoridation makes the claim that the fluoridation chemicals used are toxic and corrosive. They also claim they contain toxic heavy metals which contaminate our drinking water.

But this is simply fear mongering – relying on chemophobia, because most concentrated chemicals are toxic and often corrosive. And such claims could also be made of the other chemicals used in drinking water treatment. But the anti-fluoridation activists don’t – why pick on fluoride?

Actually, the fluoridation chemicals used are not the main source of possible toxic contamination of our water supply – yet these other chemicals are ignored by anti-fluoridationists. When we consider fluoridation in the context of the water treatment process and analytical data for the chemicals used we find the anti-fluoridation arguments baseless.

The water treatment process

The figure below provides a context for considering the chemicals used in public drinking water treatment and the stages where they are added. It’s a diagrammatic outline of Hamilton City’s water treatment plant (it still include fluoride addition – I guess they are holding off changing the diagram until after the referendum). You can see further details in  A Guide to Hamilton’s Water Supply : River to the Tap.


This is only a typical example. Different treatment plants use different chemicals depending on the plant size, the water source and the availability and cost of chemicals. I consider just a few  representative chemicals below with information on their safety, corrosive nature and chemical contaminants.

Information sources used

The safety information is from safety data sheets produced by the manufacturer or seller. Many of these are in the Orica Chemicals SDS database.

Information on contaminating heavy elements and other contaminants is from Brown et al. (2004). Trace contaminants in water treatment chemicals: sources and fate, American Water Works Association, Journal. 96: 12, 111-125.

Extra information on contaminants in fluoridation chemicals is from the NSF Fact Sheet on Fluoridation Products (2013) and the  NZ Water and Wastes Association Standard for “Water Treatment Grade” fluoride, 1997.

miscellaneous chemicals

A number of chemicals like lime, soda ash, carbon dioxide, potassium permanganate and other acids and alkalis are used, sometimes or commonly. This could be for initial treatment to remove biological matter and in pH control and sedimentation. Adjustment of pH is also necessary to prevent corrosion of pipes.

Coagulation and sedimentation

Aluminium sulphate or alum, is a common coagulant.  Its Safety Data sheet does not classify it as dangerous for transport but does classify it as hazardous – subclasses 6.1 – 9.3.

Under disposal methods it says:  “Refer to local government authority for disposal recommendations. Dispose of contents/container in accordance with local/regional/national/international regulations.”

Possible contaminants (Brown, Cornwall & McPhee, 2004): Coagulant chemicals are the main source of trace metal contamination in water treatment.” However, these together with contaminant trace metals in the source water are generally transferred to the residue stream during sedimentation and filtering so there is little transfer to the finished water.

Soda ash is used for pH control. Its Safety sheet does not classify it as dangerous for transport but does classify it as hazardous – subclasses 6.1 – 6.4.

Under disposal methods it says:  Refer to local government authority for disposal recommendations. Dispose of material through a licensed waste contractor.”


Chlorine is commonly used. Its Safety data Sheet classifies it as a class S7 dangerous poison which “must be stored, maintained and used in accordance with the relevant regulations.”

Under disposal methods it says: “Refer to Waste Management Authority. Dispose of material through a licensed waste contractor. Contact supplier for advice.”

Possible contaminants (Brown, Cornwall & McPhee, 2004)Carbon tetrachloride (used to clean storage containers)


Fluorosilicic acid is the most common fluoridating chemical. Its Safety data sheet describes it as a class S7 dangerous poison.

Under disposal methods it says: “Refer to Waste Management Authority. Dispose of  material through a licensed waste contractor. Decontamination and destruction of containers should be considered.”

Possible contaminants (Brown, Cornwall & McPhee, 2004): Arsenic was the only trace metal contaminant found above detection levels in just a few samples, and then in small amounts.

This year’s NSF Fact sheet on fluoridation  also confirmed this picture. saying:

“In summary, the majority of fluoridation products as a class, based on NSF test results, do not contribute measurable amounts of arsenic, lead, other heavy metals, radionuclides, to the drinking water.”

(NSF International is a global independent public health and environmental organization that provides standards development, product certification, testing, auditing, education and risk management services for public health and the environment.)

The  NZ Water and Wastes Association Standard for “Water Treatment Grade” fluoride, 1997 says:

“Commercially available hydrofluorosilicic acid, sodium fluoride and sodium silicofluoride are not known to contribute significant quantities of contaminants that adversely affect the potability of drinking water.”

I discussed the question of the level of toxic metal contamination in fluorosilicic acid in my article Fluoridation – are we dumping toxic metals into our water supplies? This mentions the requirement of suppliers to provide certificates of analysis to make sure their product is suitable for water treatment. A number of certificates of analysis for fluorosilicic acid are available on line which confirm the very low levels of contaminant heavy metals. For typical fluorosilicic acid certificates see Incitec 09, Incitec 08 and Hamilton City.

The table below also shows typical analytical results for fluorosilicic acid.

General conclusions

According to Brown, Cornwall & McPhee, 2004:

“Except for occasional contamination from bromate in sodium hypochlorite and carbon tetrachloride in chlorine., drinking water treatment chemicals were not typically shown to be significant sources of most contaminants of regulatory concern (including lead, copper, arsenic, and other trace metals) in finished water. This was becausc of the low occurrence of contaminants in drinking water treatment chemicals and the partitioning of most contaminants into the residuals streams when they were present in raw water or treatment chemicals.”

The recovery of sediment and sludge after coagulant treatment removes most of the toxic contaminants coming from the source water and the treatment chemicals (mainly the coagulant). No significant contamination comes from the chlorine or fluoridation chemicals added towards the end of the treatment. The table below confirms this.

The real amounts of contaminant toxic metals in fluorsilicic acid are far lower than the amounts allowed by the water treatment standards.  The regulated impurity levels are calculated from the maximum acceptable values of an impurity (taken from the Drinking Water Standards for New Zealand 1995) and the dilution when the material is added to drinking water to achieve a concentration of 0.7 – 1.0 ppm F. It incorporates a safety factor of 10. The data for the fluorosilicic acid is from my research but confirms figures in certificates of analysis. And the last column shows that there is no detectable contamination of toxic heavy metals in the final drinking water

Final drinking water quality

Toxic Element Impurity limits FSA Drinking water
As (ppm) 132 2 <0.002
Cd (ppm) 40 <1 <0.001
Cr (ppm) 660 5 <0.001
Hg (ppm) 26 < 0.1 <0.001
Ni (ppm) 264 < 1 <0.001
Pb (ppm) 132 0.3 <0.001
Cu (ppm)   < 0.2 <0.013
Zn (ppm)   2.1 <0.013

Impurity limits – calculated from maximum acceptable values in drinking water and a safety factor of 10. See NZ Water and Wastes Association Standard for “Water Treatment Grade” fluoride, 1997.
FSA – typical analytical data for fluorosilicic acid used in fluoridating New Zealand water supplies.
Drinking water – actual levels of toxic elements in your drinking water (Wellington region) – all below the limit of detection of the standard analytical procedure.

The “proof of the pudding is in the drinking” – one could say. The antifluoridation activists have been simply scare mongering with their claims that fluoridation amounts to putting toxic elements into our drinking water. The fluoridation chemicals are not even the main possible source of such contaminants.

See also
Fluoride in our water facebook page
Debunking the anti-fluoridation myths
From Australia – debunking anti-fluoridation arguments

For other articles on fluoridation see Fluoridation page.