Direct against indirect cold water: mains-fed or cistern-fed outlets, gravity pressure of about 0.1 bar per metre of head, and the trade-offs of each.
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. Both start at the incoming main and stop tap; what differs is how the water is distributed from there.
In a direct cold water system, the cold taps and appliances are fed straight from the incoming mains supply, so the kitchen tap, basin, bath and WC all run at mains pressure. The water at every cold outlet is mains-fresh, 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 in the loft, and that cistern then supplies some or most of the cold outlets by gravity. Typically the kitchen tap stays on the mains for wholesome drinking water, while the basin, bath, WC and the cold feed to the hot water cylinder draw from the cistern.
Why the pressures behave differently
Direct outlets see whatever the mains delivers, which is strong but can vary with local demand. Indirect outlets see a pressure set purely by the height of the cistern above them — roughly 0.1 bar per metre of head — so an outlet just below the loft gets a gentle flow while one two floors down gets noticeably more. That is why gravity-fed showers on the same floor as the cistern often disappoint, and why the head available matters when choosing outlets and appliances.
Advantages and trade-offs
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. Fewer outlets are exposed to mains-pressure surges or water hammer.
It has trade-offs too. The stored water must be protected to stay wholesome — lid, insulation and a screened warning pipe — and the cistern adds weight, space and a maintenance item. 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. Plenty of UK housing stock still runs indirect, so you must be able to recognise it: a loft cistern, quieter outlets, and only the mains-fed kitchen tap treated as the drinking supply. 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.