Direct and indirect plumbing systems: what’s the difference?

The difference between direct and indirect plumbing systems concerns how cold water is distributed throughout the home. In an indirect system, the cold taps are supplied by the cold water storage cistern in the loft. In a direct system, they’re supplied by the mains. Each system comes with its own set of advantages and disadvantages. In this article, we’ll go through the main differences.

Direct and Indirect plumbing systems explained

In an indirect system, the mains enters the property and branches off to supply the cold kitchen tap. It then rises up to the loft to feed the cold water storage cistern. The cold cistern supplies cold water to everywhere else in the household, such as the cold bathroom taps, and the hot water cylinder.

In a direct system, all of the cold outlets are supplied by the mains. The cold water storage cistern supplies only the hot water cylinder. Alternatively, there may not even be a storage cistern if the property has a combi boiler or an unvented hot water cylinder. Both of these appliances are fed directly from the mains.

Advantages and disadvantages

The main advantage of an indirect system is that even if the water supply to the property is cut off, there’s still a reserve of water. For example, you’ll still be able to flush the toilet until the loft cistern is empty. Indirect systems also operate at a lower pressure than mains water. They are much quieter, and less susceptible to water hammer.

The main disadvantage of an indirect system is the risk of stagnation and contamination that comes with keeping a large quantity of water open to the atmosphere. Current water regulations require cisterns to be fitted with a set of components to ensure the water remains potable, i.e. drinkable. However, the idea of brushing your teeth in water which has come from a tank in the loft may not be very appealing.

This rings particularly true in the past, when the regulations for loft cisterns were much less stringent. It was not uncommon to find dead insects, rodents, and even birds at the bottom of the tank. This is historically the reason why drinking from the bathroom taps in British homes is not recommended. In contrast, direct systems offer drinking water from every cold tap in the home. Their other main advantage is that their higher pressure means much greater flow rates.

Indirect systems obviously require space in the loft for a bulky water tank. Long, narrow “coffin” tanks are available, but in the case of a future loft conversion, a complete change of plumbing system may be necessary, for example, removing the cisterns in the loft and converting to a combi boiler system.

Hot water cylinders

So there you have it – the difference between direct and indirect plumbing systems explained. Note that direct and indirect may also refer to different types of hot water cylinder. In this context, direct and indirect refers not to how the cylinder is supplied, but how the water is heated. For more information, check the hot water cylinder page.