Which organization must approve composite materials used for the construction of portable water tanks?

The correct answer is the FDA, which stands for the Food and Drug Administration. This organization is responsible for ensuring the safety and proper labeling of food substances, including components that come into contact with drinking water. Since portable water tanks are used to store potable water, it is critical that any materials used in their construction meet the FDA's standards for safety and health.

The FDA evaluates the suitability of materials intended for contact with drinking water to prevent any potential leaching of harmful substances into the water. By ensuring that only FDA-approved composite materials are used, manufacturers can help guarantee that the water stored in these tanks remains safe for consumption.

Other organizations mentioned, such as the EPA, OSHA, and NFPA, focus on different aspects of safety and regulations. The EPA (Environmental Protection Agency) handles environmental protection and may regulate water quality but does not directly approve materials. OSHA (Occupational Safety and Health Administration) is concerned with occupational health and safety regulations, while NFPA (National Fire Protection Association) deals primarily with fire safety codes. Therefore, none of these organizations is responsible for the approval of composite materials specifically for potable water tank construction as the FDA is.