Plumbing problems

Water mains

Beads of condensation on cold pipes can be frustrating and difficult to remedy. If there is moisture in the dwelling air (which there always will be), and the mains cold pipe is cold (which it always will be), a film of moisture or chains of watery beads appear on the pipe surface. Remediation may be to replace a metal pipe with plastic, insulate the pipe or reduce the amount of moisture in the room air, so that the amount of condensate forming reduces too.

Water mains are often ignored as a potential cause of damp problems in buildings. Leaks can cause problems both inside and outside the building. A fierce water main breach can displace ground soils to destabilise a foundation, causing not just damp but a structural problem. Leaked water collecting on a pathway can ice up to form a slip hazard.

It is becoming easier to detect a mains water loss as more properties are fitted with a water meter. For properties without a meter, more traditional means of confirming leakage, such as listening sticks, may be employed. Water mains can leak for a multitude of reasons:

• bi-metallic corrosion between different metals breaks down a joint;
• pipes can be accidentally punctured;
• pipes can corrode;
• pipe joints can just pull apart; or
• joints can weep due to being poorly made.

Some copper pipework produced in times of copper material shortages is of inferior quality and could have been installed with latent flaws, meaning its service life would be very much shortened. The consequences of a water main leak can be severe, as there is a limitless supply of water from the water mains to escape via the flaw.

More and more properties are dispensing with storage facilities for water, as evidenced by the number of old tanks you see piled up in skips. Central heating systems are run directly off combination boilers, with no need for feed and expansion tanks. So more and more kitchen and bathroom taps are fed directly by mains supply and there are fewer tank leaks from the loft.

Water main leaks feature in several of the case studies. It is worth dwelling on a few pointers to good joint-making so we might avoid the predictable leaks.

The dripping stop valve

Valves that shut off water commonly use 2 basic methods.

• Some valves incorporate a washer (usually a replaceable component);
• other valves will shut off water by closing of a metal gate (e.g. a 'gate valve') or the revolving of a metal ball with an aperture through its middle (the valve successfully turning off water by virtue of a meeting of 2 accurately machined faces).

Valves that use rubber washers are often more able to completely turn off water. Gate valves nearly always allow a small dripping of water to continue, even when the gate is really tightly shut.

Two common valves are used in the domestic setting. The mains stop valve most of us are familiar with is a brass inline valve fitted with a standard tap, and often fitted with an identification label like a parcel. Many textbooks advise us all to label stop valves, but few heed the advice. Such a valve is usually turned off by hand and has a capstan head fitted to a spindle that is threaded at the end that houses a 'jumper' fitted with the washer. Turning the tap gradually pushes the spindle downwards and eventually the washer fully seals off incoming water from the mains side. This type of stop valve is designed so that, should the washer remain stuck to its seating, water pressure will force it off, so a no-flow situation cannot arise. So it is important that the valve is fitted the correct way round, with the marked arrow in the direction of flow.

Nowadays, 'service valves' are becoming more widely used; they are ball valves.

The ball has a through hole, and when the hole is in alignment with the direction of flow, water can pass through the valve. The valve is usually turned by a straight bladed screwdriver.

Traditional stop valves are used to turn off the house supply. They are a very real damp threat. The problem is the gland packing. The spindle is sealed by compacted material, and drips commonly develop around it. Sometimes the packing gland nut can be tightened to solve the drip, sometimes the gland packing needs to be replaced. Some plumbers use PTFE tape, some use wool compacted with petroleum jelly, and some hessian and plumber's pipe jointing paste. However, many stop valves are in inaccessible places, and drips may continue for weeks, months and even years. Timbers can rot from the persistent weeping of these valves.

Figure 1: On the left a 'service valve', suitable for isolating the mains supply to a WC cistern or perhaps a bathroom tap. They are not that likely to drip. To the right a traditional stop valve – that can turn off the mains. Usually found under a kitchen sink or under the stairs

Figure 2: Undo nut B and the whole inner guts of the tap can be taken out, the rubber washer levered off from its holding rivet and replaced with a new one. If the valve's seating looks rough or corroded, you can screw a reseating device onto the same female thread and 're-seat' the tap. Such a stop valve costs just a few pounds to purchase – so you can just replace it and repair the old one at your leisure

Occupiers and managers of property need to know where stop valves and service valves are located. An emergency, when the supply needs to be isolated quickly, is not the time to explore the complexities of your plumbing. Mains shut-off keys need to be kept where needed, but few householders seem to keep one handy. If water cannot be quickly turned off inside the property you may need to access the OSV (outside valve), usually located in the pavement in front of the house wall or fence. Use a large screwdriver to lift up the flap and the mains key to turn off the supply. Older valve chambers will include a pear shaped flap with the letter 'W'. If the pit is not filled with debris, you will see either the capstan head of the stop valve or an extension rod of square section. Use the mains key to turn the valve clockwise until it has turned the water off. This whole operation may be quite straightforward in a single occupancy property, but you may see in some pavements an absolute gaggle of water main flaps – and which one relates to the subject property may be very difficult to work out.

Modern water meter chambers can be opened to reveal a vertical plastic rod, for which a special shaped plastic key may be needed... an emergency may not be the time to order one!

In the author's experience, the main culprit for water main leaks does not hit the headlines, as drips from a stop valve are not dramatic events. But steady drips in concealed voids from around the spindle can amount to substantial water escapes over prolonged periods. You so often find stop valves under floors, over timber joists, and drips have seeped into the timbers and caused wet rot. Sometimes a stop valve next to a WC cistern, installed with the best intentions, may be causing rot to floorboards below as it weeps and drips, as well as damaging the floor coverings. Stop valves near kitchen units drip, and chipboard cabinets cannot usually withstand being wetted for long.

Once you have fitted a traditional stop valve, it pays to ever so slightly tweak the packing gland nut A. This will prevent drips seeping from around the spindle. Eventually, after a few years' service, tightening the nut does not stop a drip.