Before you can work on any part of a plumbing system - even if you just want to change a washer on a tap - you will have to turn off and drain the water from it. A really useful DIY tip is to divide the system into relatively short runs of pipe by adding valves.

Turn off the main stopcock to cut off the supply to the kitchen tap and every other cold tap on a direct system. Next, open the tap until the water stops flowing. To isolate bathroom taps, you'll need to close the valve on the appropriate cold feed pipe from the storage cistern and turn on all the taps in that section. Don't panic if you can't find the valve: rest a length of wood across the top of the cistern and tie the arm of the float valve to it. This will shut off the supply to the cistern so you can empty it by running all the cold taps in the bathroom. If you can't get into the loft, turn off the main stopcock then turn on all the cold taps.

First of all, turn off all immersion heaters or boilers. Next, close the valve on the cold feed pipe to the cylinder and run the hot taps. Notice that even when the water stops flowing from the taps, the cylinder will still be full. Again, if you can't find the valve on the cold feed pipe, tie up the float valve arm, then turn on the cold bathroom taps to empty the storage cistern.

If you have a direct system, you have to drain the system by running the hot taps. But if you have an indirect system, if you run the hot taps first, the water that is stored in the cistern will flush out all your hot water from the cylinder.

When the cold taps run dry, open the hot taps. In an emergency, run the hot and cold taps together to clear the pipes as quickly as possible.

The simplest way to drain the cistern alone is to tie up the float valve arm and flush. If you need to empty the pipe supplying water to the cistern, either turn off the main stopcock in a direct system or, in an indirect system, close the valve on the cold feed from the storage cistern.

Alternatively, you could once again tie up the float valve arm on the storage cistern and empty all the water out through the cold taps. Keep flushing the lavatory until no more water enters its cistern.

First of all, you need to close the main stopcock on the rising main. Next, open up all the cold water taps in the bathroom. (If you have a direct system, then you need to open the hot taps.) At the bottom of the cistern will be the residue of water, which you will need to bail out.

If your hot water cylinder has sprung a leak, or you are intending to replace it, the first thing to do is to switch off any immersion heaters or boilers. Next, shut off the cistern's cold water supply, or drain the cold water cistern. Turn on all the hot taps and drain out the water.

If your hot water is heated by an immersion heater only, you should find the drain cock on the cold feed pipe just before it enters the cylinder. Attach a hose to this and drain the water still in the cylinder into the closest drain or sink situated at a lower level.

If your hot water is heated by a boiler that is not part of the central heating system, empty the cistern with a hose from the drain cock which is on the return pipe next to the boiler.

If your hot water is heated by a central heating system, you will need to empty the cylinder via the drain cock on the cold feed pipe from the storage cistern. The primary circuit, which heats both the central heating radiators and the heat exchanger in the cylinder, are still filled with water. (The primary circuit is drained from the drain cock next to the boiler.) If you don't need to empty the radiators, shut off both valves on them.

If after all this you discover that there aren't any drain cocks, don't panic. You can still drain the hot water cylinder by disconnecting the vent pipe. The vent pipe is the pipe that enters the top of the cylinder vertically. This pipe allows for the expansion of heated water and to vent air from the system. To drain the cylinder, disconnect the vent pipe and siphon the water out of the cylinder with a hose pipe.

Whenever you modify existing plumbing or install new plumbing, your local water authority requires that certain regulations are observed. These regulations have been designed to safeguard public health and reduce water wastage. If you are making straightforward replacements, you won't have any problems, but if you are planning on adding an extra bathroom or WC, you must seek advice from your water provider and your local council. You must also ensure that you do not contravene electrical regulations. All metal plumbing must be bonded to the Electricity Board's earth terminal near your meter. If you intend to replace a section of metal pipe with plastic you may in fact break the path to the earth, so you will need to make sure that you reinstate the link. Information on the earthing system is given in our electrical section, but if you are in any doubt whatsoever, you must consult a qualified electrician.