Question

In water fluoridation, the ratio of fluoride to water is

A. 3 drops per gallon.
B. 1 part per consumer.
C. 1 part per thousand.
D. 1 part per million.

Answer 1

The correct answer to the water fluoridation question is D. 1 part per million (ppm). The fluoride ingested by someone drinking 1,920 mL of water at this concentration is 1.92 milligrams of fluoride.

Step-by-step explanation:

The student's question regarding water fluoridation concerns the optimal fluoride concentration in drinking water for preventing tooth decay, which is 1 part per million (ppm). To calculate the amount of fluoride ingested by an average person who drinks 1,920 mL of water per day at this concentration, we use the following calculation:

• 1 ppm means 1 part of fluoride per million parts of water.
  
• Since 1 liter of water is equivalent to 1,000,000 milligrams (mg), 1 ppm of fluoride in 1 liter of water is 1 mg of fluoride.
  
• Therefore, if a person consumes 1,920 mL of water (or 1.92 liters), they are ingesting 1.92 mg of fluoride (1 mg/L x 1.92 L).

Community water fluoridation, where the fluoride level is adjusted in the water supply, is the most cost-effective method to deliver fluoride to the population, reducing tooth decay by approximately 25% in children and adults.