Bathroom Plumbing & Drainage Basics

A helpful guide to aid you in understanding your homes plumbing and drainage system, while also helping you identify which water system you have.

In order to understand the plumbing in your bathroom and how it all works, it is essential to know where and how water enters and exits your bathroom and kitchen.

Your property’s mains water is supplied by your local water supplier to a stopcock located either inside or outside your property. Any problems on the suppliers side of the stopcock are their responsibility, while any problems on your side of the stopcock are your responsibility.
In the case of a leak or burst pipe, knowing the location of your stopcock can be crucial to help minimise damage in your bathroom or kitchen. There are two types of domestic water systems: indirect and direct water systems.

Indirect Water Systems

  • Most typical type of water supply system in a domestic property.

  • Work from mains water, supplied via a stopcock situated outside of your property.

  • Enters your property underground and usually surfaces near your kitchen sink.

  • An indirect water system provides fresh drinking water via the rising main and it then feeds a large water storage tank in the loft space -  this tank supplies all other domestic water requirements.

  • The feed for hot water comes via the storage tank into the boiler or heating cylinder.

  • You may have turned your mains off (turn off the stopcock, usually under the sink), but you could still get water flowing out of these tanks unless you turn off the gate valve that sits under both of them.


A stopcock to aid you when plumbing your bathroom

Direct Water Systems

  • A direct water supply system is where the raising main feeds directly the cold water taps and a multipoint water heater/boiler - so all the taps and other water feeds are at mains water pressure.

  • The stopcock for this system is normally located where the rising mains enters the house, often under the kitchen sink which is easy to find before doing soem basic bathroom or kitchen plumbing.


Water Drainage Systems

Do you ever wonder what happens to waste water once you pull the plug? Every sink or bath has a u-bend trap that retains a certain amount of water. This helps to prevent any smells drifting up from the sewer into the pipes.
If you're getting nasty smells, the solution may well be as simple as running the tap in the sink for a bit. This will fill your trap back up.
If your sink is prone to blockages (long hair combined with soap scum and skin cells will do it), it may be wise to invest in a 'snake' or a 'magic finger'. This is a flexible metal rod about three metres long. Nudge it down the drain and poke through/hook out some of the grot.

If you don't want to use strong chemicals down your sink, you can try bicarbonate of soda and vinegar to remove blockages. Wait until first thing in the morning to do this so that most of the standing water will have drained through the blockage. Throw two tablespoons of bicarb down the sink, pour a good slosh of cheap vinegar down, then put the plug in. The chemical reaction will push the blockage forward. Leave it for at least 30 minutes and then take out the plug and pour a just-boiled kettle of water down the drain.

The same principle applies for your toilet. Every time your toilet is flushed waste is forced round the bend in the bottom of the toilet. This leaves enough clean water to act as a barrier that prevents smells escaping.

Single Pipe and Two Pipe System

There are two types of drainage systems: single stack and two pipe systems.

Single pipe system

  • One large pipe that’s connected to the underground drain. All waste from upstairs basins, showers, baths and toilets will run through here.

  • Downstairs waste from sinks and basins mostly empty straight into a drain

  • A downstairs toilet will usually enter a soil stack pipe before entering an underground sewage pipe. The stack pipe goes vertically up the house to guttering level to allow venting of the pipe.


Two pipe drainage system

  • Consists of a pipe that takes toilet waste directly into the sewer. The pipe extends to guttering level that helps to vent sewer gases.

  • Bath and basin wastes are discharged independently.

Drainage Responsibility

Responsibility for maintaining drains is usually down to the homeowner. If you live in a semi-detached property, a block of flats or your home was built pre-1937; it can be a little more complicated. You can always contact your local authority who will be able to tell you who is responsible for your drainage system.

Two stopcocks to turn off the water during bathroom plumbing

How to Turn off Your Stopcock

It may sound obvious, but before you attempt to have any work done in your bathroom you must be able to turn off your stopcock. Your stopcock can be located under or near your kitchen sink. You may find that you have two stopcocks next to each other. One will not work, and is likely to have been left behind from a former plumbing job. Test to find out which one works by turning them on and off.

To close a stopcock, simply turn it clockwise.


Caring for your Stopcock

Stopcocks aren't just for Christmas. Give yours a spray of WD40 every now and again, and keep checking it. They need some TLC as they can become quite brittle over time, and may not be easy to turn off and on.


Isolation Valves

It's often the case that you don't want to turn off your whole mains for small jobs, such as fixing a dripping tap. So under sinks, attached to taps, there are usually isolation valves (sometimes called 'service valves'). 

Stopping the flow of water from your taps is really easy. Look at the isolation valve. You can see what looks like a slot-headed screw. If the slot is parallel with the arrow on the valve, the water is flowing through the pipe. To stop it, take a flathead screwdriver and turn the slot 90 degrees (a quarter turn) so that it's perpendicular to the arrow.

Isolation valves should be attached to every water-using appliance or fixture in your house, so you should be able to see them under taps, dishwashers, washing machines, toilets, showers, etc.

Be aware that isolation valves can vary in size, but they all work the same way.


A Final Word...

Hopefully this guide has helped to give you a better understanding of your homes plumbing system. If you have any plumbing queries we recommend seeking professional advice from a fully trained plumber.


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