Preliminary Treatment is the type of treatment that should be given to the water when the dilution factor is 400.

Explanation:

1. Dilution Factor:
The dilution factor is a measure of the degree to which a substance is diluted in a solution. It is calculated by dividing the volume of the substance by the total volume of the solution. In this case, the dilution factor is 400, which means that the substance is diluted 400 times in the solution.

2. Preliminary Treatment:
Preliminary treatment is the first step in the treatment process for water. It involves the removal of large particles and solids from the water before it undergoes further treatment. The purpose of preliminary treatment is to protect downstream processes, such as sedimentation and filtration, from clogging and damage.

3. Sedimentation and Flocculation:
Sedimentation and flocculation are processes used in water treatment to remove suspended particles and solids from the water. Sedimentation involves allowing the water to settle, allowing the heavier particles to settle at the bottom. Flocculation involves the addition of chemicals that cause the particles to clump together, making them easier to remove.

4. Complete Treatment:
Complete treatment refers to the entire water treatment process, which includes preliminary treatment, sedimentation, flocculation, filtration, disinfection, and other processes. It is a comprehensive approach to treating water and ensuring its safety for various uses.

5. No Treatment:
No treatment refers to the lack of any treatment processes for the water. This means that the water is not being treated or purified in any way.

Conclusion:
Based on the dilution factor of 400, the type of treatment that should be given to the water is preliminary treatment. This involves the removal of large particles and solids from the water before it undergoes further treatment. Sedimentation, flocculation, and complete treatment are not necessary at this stage.