**Core Concept**
The normal water fluoride level is a critical public health parameter that determines the risk of dental fluorosis and skeletal fluorosis. The optimal fluoride concentration in drinking water is essential to prevent these conditions while minimizing the risk of adverse effects.

**Why the Correct Answer is Right**
The optimal fluoride level in drinking water is generally considered to be between 0.7 and 1.2 mg/L. This range is based on the prevention of dental caries and the minimization of the risk of dental fluorosis. The optimal level is often cited as 1.0 mg/L, which is the recommended level by the World Health Organization (WHO). This level allows for the optimal balance between caries prevention and the risk of adverse effects.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a water fluoride level below 0.7 mg/L may not provide adequate protection against dental caries. **Option B:** This option is incorrect because a water fluoride level above 1.2 mg/L increases the risk of dental fluorosis and skeletal fluorosis. **Option C:** This option is incorrect because it does not specify a valid range for optimal water fluoride levels.

**Clinical Pearl / High-Yield Fact**
A memorable fact is that the optimal water fluoride level is between 0.7 and 1.2 mg/L, with 1.0 mg/L being the recommended level by the WHO. This fact is essential for public health professionals and clinicians to provide optimal dental care and prevent adverse effects of excessive fluoride consumption.

**Correct Answer: C. 0.7 - 1.2 mg/L**