Introduction to Plumbing Systems

The Rising Main

The main ‘artery’ of any household’s plumbing systems is the service pipe, more commonly known as the rising main. This connects the domestic plumbing system to the local water authority’s mains which runs under the pavements. The householder’s responsibility for the rising main begins at the water authority’s stop-cock, usually found in a pit in the footpath outside the house, which can only be turned on or off with one of the authority’s special shanked turn-keys. The rising main may be of lead in older buildings but most authorities have now replaced these with copper.

The rising main enters the house through the kitchen floor, generally under the sink. Just above the floor, at the base of the pipe, is the house-holder’s stopcock. This is often combined with a drain cock that will allow you to drain the rising main if you need to. Stop cocks have arrows engraved on their bodies, pointing to the line of flow.

Direct and Indirect Systems

In many older properties, mains water is supplied under mains pressure to all cold water taps and WCs, while hot water is fed indirectly from a storage cistern via the hot water cylinder. This is known as a direct system. It has the advantage that pure, clean drinking water can be drawn from any cold tap in the house and, because the storage tank in the direct system only has to provide water for the hot water system, it only needs to be a small one, holding 114 litres (25 gallons) and taking up very little space.

Most modern homes, however, are plumbed using the indirect system. Water under mains pressure enters the house through a service pipe and goes via a rising main directly into a cold water storage cistern which is normally situated in the roof space. A branch pipe from the rising main supplies pure drinking and cooking water to the kitchen sink only. (Another pipe may be ‘teed off’ from the rising main to supply water to an outside tap or garage and, if this is the case in your home, this pipe should also have its own stopcock to enable you to turn off the external water supply and drain the pipe during frosty weather.) All the other cold taps are fed indirectly and under gravity pressure from the storage cistern.

The storage cistern also supplies cold water to the hot water storage cistern which is heated either indirectly by the central heating system or by electric immersion heaters. Hot water is drawn off from the top of the cylinder to hot water taps in the kitchen and bathroom. The indirect system needs a larger cistern of at least 227 litres (50 gallons) capacity. Older cisterns were made of galvanized steel, but today most are made of reinforced plastic or polythene, which are lighter and not subject to corrosion.


Drainage falls into two categories: that above and that below ground. The drainage system above ground consists of pipework from sinks, WCs, baths and gutters.

Below ground, the services are known collectively as ‘drains’. Where a house is drained individually, the entire system, up to where it joins the sewer, is the responsibility of the householder. Where a house is connected to a communal drainage system linking several houses, the arrangements for maintenance are not quite so clear cut. If the drains were constructed before 1937, the local authority is responsible for cleansing, but it can also reclaim the costs of repairs to the communal system from the householders. If the drains were constructed after 1937, the entire responsibility for repairs, cleansing and maintenance falls to the house-holders collectively.

Fitted to the pipes entering the drains are ‘traps’. These act as water seals which prevent foul sewage air entering your home. The simplest form of trap is the familiar ‘U’-bend in the pipe which is designed to contain water after the appliance has been used. Your lavatory also has a built-in trap. Baths, basin and sinks have traps fitted between them and their waste outlets. Because of their shapes, traps with horizontal outlets are called P-traps and those with vertical outlets are called ‘S’-traps. The seal of the trap is the vertical distance between the normal water level in the trap and the upper part of the ‘U’-bend. In a two-pipe drainage system traps normally have a 50mm (tin) seal while in the single-stack system the traps need deeper seals of 75mm (3in).

Depending on how old your house is, it will either have a two-pipe or a single-stack system. The two pipe-system is the older type and is more common, but similar methods are still used to maintain both systems.

Gutters & Down Pipes

Rainwater is collected in the gutters along the line of your roof and is discharged into drainpipes. In some areas, householders are encouraged to collect rainwater in water butts for use in the garden, or they may be required to provide a soakaway to limit the amount of rainwater that collects on the surface of ground.

A soakaway is a pit not less than 3m (10ft) from the house, about 1.5m (5ft) or more deep and 1.5m sq. (5sq.ft) in plan. You can also buy perforated concrete rings from most builders’ merchants with a cover to fit into your pit. In either case, the pit is then filled to within about 300mm (12in) of the surface with hard-core and the surface soil is replaced. Under the gully there is a pipe which collects the rainwater and feeds it to the soakaway, which then allows it to slowly percolate into the soil.

Cesspools & Septic Tanks

Not all country homes are connected to public sewers. Instead, waste is drained into a cesspool or septic tank. Current building regulations stipulate that cesspools should have a mini-mum capacity of 18cu.m (4000 gallons) but many older properties have much smaller ones that require pumping out every two weeks or so.

A septic tank is a complete waste disposal system in which the sewage is broken down very efficiently by bacterial action. A heavy sludge falls to the bottom of the tank while the relatively clear water with a thin layer of scum, floats on top. A dip-pipe discharges waste below the surface so that incoming water does not stir up the sewage.

The bacteria take around 24 hours to do their magic, so septic tanks are divided into chambers by baffles to slow down the movement of sewage through the tank. Partly treated waste passes through another dip-pile into a filtration system which allows more bacterial action to take place before the water is discharged into a local waterway or is distributed under-ground, through a network of drains which allow the water to filter through the soil.

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