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.
A direct system supplies cold outlets from the incoming main. An indirect system uses a storage cistern for some outlets. The diagram shows a common indirect arrangement: the kitchen drinking tap remains on the rising main while other outlets draw from storage. Trace the pipes in the actual house: not every house follows that layout.
Pressure and flow are different
A direct outlet gets whatever pressure and flow the main provides, less the losses through the supply pipe and fittings. Mains pressure is not always high, and it varies with demand. A pump is not a free fix for a weak supply: under regulation 5 of the Water Fittings Regulations, a pump or booster that can draw more than 12 litres per minute (0.2 litres a second) from a supply pipe must be notified to the water undertaker, and work may not start without its consent.
For an unpumped cistern-fed outlet, static pressure depends on the vertical distance from the stored water surface to the outlet. Each metre gives approximately 0.1 bar. When water flows, pipe and fitting resistance reduces the pressure available at the outlet.
Worked example: a water surface 3 metres above an outlet gives about 0.3 bar static head. You will not get 0.3 bar while a shower is running. Check the shower's required working pressure and flow, the pipe route and any simultaneous demand.
What storage can and cannot do
A correctly sized cistern can cover a short drop in the incoming flow. It holds a limited reserve: it is not an endless supply, and it does not boost pressure. Its usable volume, refill rate and height must suit the outlets’ demand. Too much storage lets water stagnate, so do not fit a bigger cistern just because there is room.
A direct system needs no cold-water storage, but it has no stored reserve either. Neither layout is always better: choose the one that suits the supply and the fittings it serves.
Protect the water quality
Stored water must stay fit for its use. Protect the cistern from contamination with the right inlet and backflow arrangement, a cover and insulation, and maintain it. Being on the mains does not mean the fittings after it are clean or properly protected.
Cistern water is not unsafe by definition, and not every bathroom tap is a drinking outlet. Find the supply meant for drinking and check its quality and arrangement. G1 separates drinking and washing supplies from flushing water of suitable quality.
Recall check: on the diagram, which outlet remains available directly from the rising main? The kitchen tap. Which outlets have a storage reserve? Those connected to the cistern, for as long as the usable stored volume lasts.