Final answer:
Community water fluoridation is the most reliable source of dietary fluoride, as it is added to the public water supply to prevent tooth decay.
Step-by-step explanation:
The most reliable source of dietary fluoride is community water fluoridation. Community water fluoridation is when fluoride is added to the public water supply at a controlled level to help prevent tooth decay. It is considered the most cost-effective method of delivering fluoride to all, and it has been shown to reduce tooth decay by 25% in both children and adults.