When marking out the locations of outlets in cisterns, what is the correct order for supplies to hot water and cold water systems?

• A. Cold water below hot water
• B. Hot water below cold water
• C. Side by side
• D. Cold water above hot water

Answer: (A)

Water in a storage cistern separates by temperature because cold water is denser than hot water, so the cold layer sits lower and the hot layer rises to the top. When you’re marking outlets for supplies to hot and cold systems, you want the cold-water outlet to be lower and the hot-water outlet higher. This setup lets you draw hot water from the upper, hotter portion and keeps the cold supply reliably from the lower portion, reducing mixing between the two and preserving proper flow to each system. Putting cold above hot would disrupt the natural layering and could lead to drawing cooler water from the top or mixing hot and cold more easily. Side-by-side would not take advantage of the natural stratification and could complicate distribution.