Basis of Plumbing

Plumbing follows the basic laws of nature - gravity, pressure, water seeking its own level. Knowing this, you can understand its "mysteries" and make dozens of fixes to your home's plumbing system. You can save yourself time, trouble, and money!

The plumbing system in your home is composed of two separate subsystems. One subsystem brings freshwater in, and the other takes wastewater out. The water that comes into your home is under pressure. It enters your home under enough pressure to allow it to travel upstairs, around corners, or wherever else it's needed. As water comes into your home, it passes through a meter that registers the amount you use. The main water shutoff, or stop, valve is typically located close to the meter. In a plumbing emergency, it's vital that you quickly close the main shutoff valve. Otherwise, when a pipe bursts, it can flood your house in no time. If the emergency is confined to a sink, tub, or toilet, however, you may not want to turn off your entire water supply. Therefore, most fixtures should have individual stop valves.

Water from the main supply is immediately ready for your cold water needs. The hot water supply, however, requires another step. One pipe carries water from the cold water system to your water heater. From the heater, a hot water line carries the heated water to all the fixtures, out-lets, and appliances that require hot water. A thermostat on the heater maintains the temperature you select by turning the device's heating elements on and off as required. The normal temperature setting for a home water heater is between 140 degrees F and 160 degrees F, but 120 degrees F is usually adequate and is also more economical. Some automatic dishwashers require higher temperature water, though many of these have a water heater within them that boosts the temperature another 20 degrees F.

In order to understand plumbing and how it works, it's essential to know where and how the water enters and exits your property, and what happens to it while it's in there. The mains water is supplied by the local water supplier to a stopcock either just inside or just outside your property boundary, via a mains stopcock. Any problems on the supplier's side of the stopcock are their responsibility, while any problems on your side of the stopcock are your responsibility.

Domestic Water Systems

There are basically two types of domestic water systems - indirect water systems and direct water systems. Indirect is a mains-fed, stored-water system that supplies the drinking water then runs into a water tank in the loft which feeds all other water outlets.

Direct is also a mains-fed system but it feeds all the taps with mains water pressure and provides drinking water from any cold-water tap in the house. This is a great system, especially is you're contemplating a lost extension, as it does away with water storage tanks. It's also very handy if you happen to get thirsty in the night - you don't have to go all the way to the kitchen tap for a drink, just pop into the bathroom. The other advantages are that it's cheaper to install than the indirect system and you do not have to worry about the possibility of a water tank in the loft freezing and the flooding the house. A direct system requires a pressurized, unvented cylinder to store the hot water. However, for this system to work successfully you need good (strong) mains water pressure.

Indirect Water System

The most common household system is the indirect stored-water system. This works from a mains supply from the company stopcock outside, which enters the house underground and usually surfaces near the kitchen sink. It supplies fresh drinking water under mains pressure, then travels via rising main pipework to a large water tank in the loft space. This tank basically supplies all your water requirements other than fresh drinking water: usually a washbasins, baths, toilets and showers. The feed for the hot water comes via the storage tank to the boiler or heating cylinder. The water level within the tank is controlled by a floating ball valve which automatically shuts off the water supply at the pre-set level. An overflow pipe fitted to the tank prevents flooding as a result of ball valve failure. Water pouring into the garden from the overflow pipe will quickly alert you to a ball valve problem. This is easily solved, usually by replacing a simple washer on the valve in the storage tank.

Direct Water Systems

Here, the water supply comes in from the outside stopcock via the mains pipe, which runs beneath the house and surfaces near the kitchen sink. The kitchen is the first port of call because the strongest demand for water is here, and the kitchen sinks tap is traditionally where fresh drinking water is supplied. The mains pipe then rises to feed the boiler for the hot-water supply and all the cold-water taps in the bathroom. The toilet is also fed by, mains pressure. The boiler feeds the unvented cylinder, and the hot water (under pressure) feeds all the hot water taps in the house. Any secondary bathrooms will be supplied in the same way.

Bathroom Tip: If you're planning to fit a boiler and cylinder, check that the sizes you are fitting are adequate for meeting the hot water requirements of your household, including any future expansion in demand, such as loft of kitchen extensions, or maybe an en-suite bathroom.

Drainage and waste systems

Three types of plastic can be used for external drainage and waste pipework. Acrylonitrile butadiene systems (ABS) is a very tough plastic that can be used for both hot and cold waste. It can be connected using either solvent or compression joints. Polypropylene (PP) is a softer, more flexible plastic. It is impossible to glue PP, so the connections are always made using push fit joints. The most commonly used material for external waste pipes is unplasticized polyvinyl chloride (UPVC). This type of plastic is damage resistant to most kinds of household products like bleach and washing powder. Although plastic pipes have been around for many years, until recently the most successful type has been waste pipe made from hard plastics. Plastic supply pipe (cold water) has now been introduced for use underground. Coloured blue, this medium-density polythene (MDPE) pipe is pressure- and corrosion-resistant, thank goodness, so you can fit it and then forget about it. Old mains pipes were quite often made of galvanized steel or lead, which eventually deteriorated. If you have a leaking old-style mains pipe on your property, make sure that you replace it with medium-density polythene. It is far more efficient than the old metal pipes and doesn't rot.

Waters Systems

Once water enters the property, where does it all go every time you pull the plug on the washing-up, empty the bath or flush the toilet? Underneath every sink or bath there is a U-bend trap, which always retains a certain amount of water, preventing unpleasant sewer smells drifting back up the pipe – the water acts as an impenetrable barrier for such smells. The same principle is used for the toilet –each time it is flushed, everything is forced round the bend in the bottom of the toilet, leaving enough clean water to act as a barrier that prevents smells.

Single Stack

There are basically two types of drainage systems – a single stack or pipe, or the more common two-pipe system. In the former, all the soiled water and toilet waste enters a 100mm (4in) diameter soil stack pipe before running into the underground sewage pipe system via a manhole inspection chamber. This chamber allows for rodding to dislodge any blockages. The stack goes up to eaves level . (guttering) to allow venting of the pipe. This single stack has to be well planned to prevent siphoning of any traps elsewhere in the system, which would allow smells or ever sewer rats into the drainage of your house.

Two pipe System

More common is the two-pipe drainage system, which is generally pre-1960s. This consists of a 100mm (4in) diameter pipe that takes the toilet waste directly via the manhole inspection chamber into the sewer. The pipe also extends to roof level to vent sewer gases and to prevent siphoning the water from the toilet trap. Bath and washbasin waste are often discharged into a smaller vertica pipe via an open hopper leading to a gully, into which the kitchen sink discharges independently. The gully branch enters the manhole inspection chamber, adjacent to the toilet waste branch, before heading off to join the main sewer. Again, the purpose of the inspection chamber is to allow access for rodding to clear any blockages.

Drainage Responsibility

Responsibility for maintaining drains up to the main sewer is usually the owner's. A block of terraced or semi-detached properties is often more complicated. If the properties were built pre-1937, the local authority is responsible for the cleansing, but if repairs are required, local authorities are empowered to reclaim the costs from the householder. Contact your local authority's technical services department to find out who is responsible for your drainage system.

Decades ago, installing a drainage system was a complex and skilled job that involved working with cement joints, salt-glazed clay pipes and fittings, and brick manhole inspection chambers. Today, most local authorities accept modern plastic pipes and inspection chambers, putting drainage well within the capabilities of the bathroom DIY enthusiast. Always check with your local authority before starting drain work, and have the work inspected and approved before reinstating the ground.

Fitting and positioning pipes

Any pipe that discharges into a gully should extend down into the gully below the grille by about 50mm (2in). The reasons for this are twofold. If fallen leaves or rubbish cover the gully grille, water that is discharged from the house will be prevented from entering the underground drainage system. Also, when washing machines or baths discharge, there is a sudden exodus of water, and if that discharged water is not completely contained within the gully, serious problems may occur. Where water softens ground around and under the foundations of a building, for instance, undermining may result, which can cause major cracking. So make sure that all waste pipes extend into the gully, and that there is a suitable mortar seal between the gully and surrounding surface.

Turning off the water

This may sound like stating the obvious, but turn off the water before you attempt to do any work in the bathroom. Locate the relevant valves and turn them off - there is normally a main stopcock under or near the kitchen sink 1. On older, unimproved properties, this may be the only valve for the whole plumbing system; if so, you will have to turn this off and drain down the system by opening all the taps and flushing the toilet until the storage tank is empty.

Bathroom Tip: To temporarily restrict the tank in the loft from refilling, lay a wooden batten across the top of the tank, and tie the ball valve float to it. With the valve closed, open all the taps to empty the tank. Remember, this is temporary, until you fit a gate valve.

Gate Valves

You can avoid the need to empty the storage tank each time you work on the water system, and also keep the cold mains on, if you fit gate valves to both the cold feed pipes leaving the tank 2. This straightforward job will enable you to leave the cold supply to your kitchen for fresh drinking water and cooking, even while you isolate the bathroom for carrying out repairs and alterations. And you won't need to wait for the empty storage tank to refill afterwards.