A stopcock usually leaks from around the spindle, where the handle turns, or from the joints where it connects to the pipe on either side. Worn seals or packing, loose fittings, corrosion and occasionally a cracked valve body can all cause a leak.
Where the water appears can give a useful clue about which part may be at fault. Because the stopcock controls the water to the whole property, a leak here is worth dealing with promptly.
Leaks Around the Spindle
The spindle is the part that turns when you move the handle. A seal or packing around it stops water escaping. Over time this can wear or dry out, so water may seep out, especially when the stopcock is turned.
WaterSafe notes that a leak from the spindle often points to an issue with the gland nut, the nut that holds this seal in place. A spindle leak may be slow at first, but it can get worse, particularly if the stopcock is used after a long time without moving.
Some spindle leaks only appear after the stopcock has been turned, because moving it can disturb an old seal that had settled in place.
Leaks From the Joints
Many stopcocks are connected to the pipe with compression joints, which use nuts and rings to make a seal. If these loosen or wear, water may appear around the joints either side of the valve. Pipes that move or are knocked, such as in a busy kitchen cupboard, can make this more likely.
Water at a joint does not always mean the joint itself has failed. It may be running along the pipe from somewhere higher up.
Corrosion or Damage
Older stopcocks may show green or white deposits, rust or pitting. In some cases corrosion can weaken the body of the valve. A cracked body, a damaged handle or a stopcock that has been forced in the past may also leak.
In these cases, a repair may not be practical and replacement may need to be considered. That depends on what is found.
What to Do About a Leaking Stopcock
Take a photo of where the water is coming from, as this can help when you describe the problem.
Place a bowl or towel under the leak and keep the area clear. Avoid tightening nuts hard or taking the stopcock apart, as it is part of your water supply and is under mains pressure. If the stopcock is stiff, do not force it, as this could make the leak worse.
If the leak is getting worse, your water supplier may be able to advise on the outside stop tap, which may be the only way to isolate the supply.
Our page on stopcock repair in Poole explains how leaking and faulty stopcocks are assessed and repaired.
If your stopcock is leaking, a plumber can check the cause and explain whether a repair is suitable.