What is the recommended method for rechlorinating a 400-gallon water trailer?

The recommended method for rechlorinating a 400-gallon water trailer involves using 5 half-gram spoonfuls of calcium hypochlorite with one half canteen cup of water. This method effectively ensures that the necessary concentration of chlorine is achieved for disinfection purposes.

Calcium hypochlorite is a commonly used disinfectant due to its ability to kill bacteria and pathogens, making it suitable for treating potable water. The selected ratio in choice B is designed to ensure an adequate level of chlorine is present to sanitize the water while also being manageable for mixing and application. This method helps to create a chlorine solution that can be evenly distributed throughout the larger volume of water.

The specified amount also takes into account factors like the dissolution rate of calcium hypochlorite and the efficiency of chlorine disinfection without over-chlorinating, which could lead to unpleasant tastes or possible health concerns. This careful balance of quantity and method supports the goal of maintaining safe drinking water standards in military settings, where field sanitation is crucial.

By using the correct quantity of calcium hypochlorite dissolved in water, the answer aligns with established guidelines for water treatment in such environments, ensuring that soldiers have access to safe and potable water.