In the case of fluoridation of drinking water, doubt may be cast on the balance of its costs and benefits by singling out adverse consequences of high levels of fluoride in water or the possibility that fluoride in water might combine with fluoride form other sources, such as food. For example, the web site of the Safe Drinking Water Coalition[1] calls for and end to fluoridization of water and cites in support a US NRC report from 2006.[2] This report argued that the US Environment Protection Agency standard of a maximum 4mg/L of fluoride in drinking water was too high. However, the report in question explicitly did not assess the policy of fluoridating water, where natural concentrations of fluoride were low. Fluoridization policies aim to set levels of fluoride of 0.7 to 1.2 mg/L, which is much lower than the EPA safety threshold.

Nevertheless, the Safe Drinking Water Coalition cites personal opinions in support of abandoning the practice of fluoridation of drinking water, which are offered by some investigators on the panel making the assessment of EPA standards.[3] It could also have cited the opinion of a Nobel Laureate, Arvid Carlsson. Its call to stop fluoridation of drinking water thus, not only relies on distortion of the findings of the report, but also invokes scientific doubts as to its safety. These doubts may be perfectly legitimate in the context of theoretical enquiry, but it does not follow that practical doubt is equally reasonable.

To establish the latter requires an assessment of the likely improvement in dental health from the policy over and above improvements from other sources, such as fluoride in toothpaste, balanced against any health risks of excessive intake of fluoride, and taking account of whether individual action should be preferred to collective action. So far, the scientific consensus is that fluoridation of drinking water has important benefits and that a real possibility of very serious adverse health consequences has not been established. Universality of protection may be cited as a reason for collective action rather than relying on individual use of fluoride toothpaste. Nevertheless, while there is a scientific consensus that improvement in dental hygiene is associated with water fluoridation, there is not yet a scientific consensus on whether fluoridation of water has decisive advantages over use of fluoride in toothpaste, at least for any benefit over and above the advantage of providing universal protection to children.

Compulsory vaccination for rubella, measles and mumps has been challenged on the grounds that it leads to autism, neurological disorders, and sudden death syndrome in infants. The scientific consensus is that there is no epidemiological evidence to establish a causal relationship or warrant for precautionary measures. Here the evidence for purposes of practical decision is complicated by the fact that concerns about vaccination have been concerns about death or serious disease. These outcomes prompt the use of precautionary reasoning, as they do in criminal trials.