Lithium, a powerful mental health treatment, could be added to water supplies by New Zealand's local councils under the same vague rules that allow them to add fluoride.
That was one of the arguments anti-fluoridation group New Health NZ put to a test court case being heard in New Plymouth today to decide if South Taranaki District Council has the right to put fluoride into water supplies at Patea and Waverley.
Such an idea was once floated in the US, the group's barrister, Lisa Hansen, told the High Court, at what is expected to be a two-day hearing that may ultimately decide the future of the fluoridation debate.
One of her key arguments was that New Zealand has no law allowing councils to introduce fluoride, and the practice is merely a convention established by a court case half a century ago.
She said fluoridation was a therapeutic action, unlike adding chlorine to make water safe, and its use denied people the right to choose whether they wanted to take a medication - one that was highly unlikely to benefit them.
After listening to an hour and a half of historical, scientific and medical submissions from Ms Hansen, Justice Rodney Hansen (no relation) advised her that the hearing needed to move on to the legal issues, as he was in no position to settle all the unresolved scientific and medical issues.
Ms Hansen maintained her position that it was important for the judge to hear historical aspects of the fluoride debate, but took Justice Hansen's hint and switched to key legal points in the case.
As the plaintiff, New Health began the hearing - attended by a dozen spectators - by referring to a massive pile of documents that it would submit as evidence.
Ms Hansen reminded the court a leading court case on fluoridation happened exactly 50 years ago when Lower Hutt City Council was challenged over the practice, which began in New Zealand in 1954 in Hastings.
The case went to appeal and eventually to the Privy Council in London, with the council winning, thus establishing a general and implied power to councils.
Today, 48 per cent of New Zealanders lived in communities with fluoridation, put into water supplies by 22 of the country's 67 local authorities. However, today's context was quite different, legally, ethically and in terms of the science, she said.
Ms Hansen referred to research that showed fluoride taken via the water supply did nothing to prevent tooth decay because the method did not provide enough of the element to make an impact.
On the other hand, gels and toothpaste containing fluoride could have a beneficial effect. They provided "topical" (local) protection, rather than the "systemic"(ingested) approach used by fluoridation.
Excessive fluoride carried risks of dental fluorosis, which could leave teeth chalky and mottled. One research outcome showed fluoridation doubled the incidence of this complication, she said.
Where fluoridation was used overseas, it was done so under a statute, but New Zealand did not have that.
If fluoridation was ever to be lawful, there would need to be a specific provision to permit it and no other substances, such as lithium or contraceptives.
Her first legal argument concerned a council's powers under local government and health statutes.
Ms Hansen maintained the use of fluoridation amounted to a regulatory function, and as such was a legislative one beyond the powers of local councils; one held by Parliament.
She then traversed the Bill of Rights Act and provisions protecting a person's right to autonomy and self-determination, which were breached by fluoridation.
Nobody living in a community where water was fluoridated could escape it, unless they stayed at home and produced their own food, she said.
Further, fluoridation amounted to a medical treatment under New Zealand legislation and should be subject to provisions of medical statutes. By the same argument, the fluoride compounds used by councils were legally medicines, Ms Hansen said.
The hearing continues, with arguments yet to be heard by the defendant council, represented by Duncan Laing and Hamish Harwood.
The Crown Law Office is represented by Austin Powell, who is keeping a watching brief for the Attorney-General, and who is expected to make submissions on human rights aspects.
Justice Hansen wanted to know why there was still a case for advocating fluoride in water supplies if the plaintiff's submissions were to be believed.
On the basis of the New Health data, it was a wonder there was anyone left in the world still in favour of the practice, so on what context was it supported by some academics, he asked.
Ms Hansen said this was why the historical context of the controversial practice was important. Fluoridation was hailed as a great medical success of the 20th century, and it was adopted in New Zealand as a result of institutional bias in its favour.
Justice Hansen asked whether it was based on scientific studies or just plucked out of the air.
Ms Hansen replied that a UK review in 2002 found the widespread adoption of fluoridation was founded on poor-quality research: ``We are asking the court to consider the more contemporary knowledge we now have.''
Duncan Laing began his submissions on behalf of the council just before the hearing closed for the day.
It continues tomorrow.