The difference between a direct and an indirect cold water system and why a property uses one or the other.
Cold water can reach the taps in two broad ways, and Level 2 expects you to tell a direct system from an indirect one and understand why each is used.
In a direct cold water system, the cold taps and appliances are fed straight from the incoming mains supply. The water at every cold outlet is therefore mains-fresh and at mains pressure, and the only stored water, if any, is a small feed to a hot water system.
In an indirect cold water system, the mains feeds a storage cistern, usually high up, and that cistern then supplies some or most of the cold outlets by gravity. Typically the kitchen tap stays on the mains for drinking water, while other outlets draw from the cistern.
The indirect approach has clear advantages. The cistern is a reserve if the mains supply is interrupted, the pressure to the cistern-fed outlets is steadier and gentler, and the stored feed evens out demand on the main.
It has trade-offs too. The stored water must be protected to stay wholesome, the cistern adds weight, space and a maintenance item, and gravity-fed outlets have lower pressure than mains-fed ones, which affects appliance choice.
Backflow and protection thinking differs between the two, because mains-fed outlets connect directly to the supply while cistern-fed ones sit behind the air gap at the cistern. When you meet a system, identify which type it is first, since that tells you where the stored water is, what pressure each outlet has, and where the protection sits. Confirm the specifics against the current water fittings guidance.