**Core Concept:** Water fluoridation is the process of introducing fluoride ions into drinking water to prevent dental caries through reducing demineralization and promoting remineralization of tooth enamel. Methods for fluoridation can be categorized into manual and electric-assisted methods.

**Why the Correct Answer is Right:**
The correct answer, **C. Manual fluoridation**, does not involve the use of electric assistance for water flow. This method typically involves adding fluoride supplements to the water manually using fluoride-containing tablets, drops, or solutions.

**Why Each Wrong Option is Incorrect:**
A. **Electrical fluoridation (Option A)** uses electric energy to increase water flow and fluoride concentration in drinking water. This method is considered electric-assisted and not the correct answer.
B. **Manual fluoridation (Option B)** is another method of adding fluoride to water manually using fluoride supplements. However, this option is incorrect because it is not specifically mentioned as not depending on electric assistance.
D. **Self-contained fluoridation system (Option D)** is another type of electric-assisted water fluoridation method, involving a self-contained unit that provides both fluoride and water at the desired concentration. This option is also incorrect because it is an electric-assisted method.

**Clinical Pearl:**
Manual fluoridation is a practical and cost-effective method for fluoride supplementation in communities with limited resources, as it does not require electric equipment or infrastructure. This method is commonly used in developing countries and rural areas where access to electric-assisted systems may be limited.

**Correct Answer:** C. Manual fluoridation

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A better understanding of different methods of water fluoridation helps healthcare professionals recommend the most suitable approach to their communities based on resources and infrastructure available.