Electric Shock from a Tap? Causes and Emergency Response

Getting an electric shock from a tap is alarming — and it should be. It means that metalwork in the property which should be at earth potential has become energised. There is a voltage on the pipework, and when you touch the tap (especially with wet hands), current flows through your body to earth.

The shock can range from a mild tingle to a severe jolt, depending on the voltage, the resistance of the fault path, and your own body resistance (which drops significantly when wet). In the worst cases, electric shock from water contact can be fatal.

There are four main causes, and understanding them is critical for both homeowners and electricians:

The immersion heater is the single most common cause of electric shock from taps and pipework. It works by immersing an electrical heating element directly in the water inside the hot water cylinder. The element consists of a resistive conductor inside a sealed metal sheath — the sheath keeps the electrical conductor isolated from the water.

Over time, the element sheath can corrode (especially in areas with hard water or high mineral content), develop hairline cracks, or the internal insulation can break down. When this happens, the live conductor makes contact with the water. The water becomes energised, and because the water is in direct contact with the copper pipework, all connected metalwork — hot water pipes, taps, radiators, towel rails — becomes live.

If the immersion heater element has failed, it must be replaced. The replacement element should be a direct equivalent (same length, wattage, and thread size), fitted with a new fibre washer, and the circuit should be upgraded to include 30mA RCD protection if it does not already have it.

Main protective bonding is one of the most critical safety measures in any electrical installation, yet it is frequently found to be missing, disconnected, or inadequate — particularly in older properties that have never had a full EICR inspection.

Under BS 7671 Regulation 544.1.2, the main protective bonding connection to any extraneous-conductive-part (gas, water, or other metallic pipework or service) shall be made as near as practicable to the point of entry of that service into the premises. The bonding conductors must be connected between the main earthing terminal and the following extraneous-conductive-parts:

The minimum bonding conductor size is determined by Regulation 544.1.1 and depends on the earthing arrangement. Where PME (TN-C-S) conditions apply, the conductor shall be selected in accordance with the PEN conductor CSA and Table 54.8 — typically 10mm², 16mm², or 25mm² copper depending on the supply. Where PME does not apply (TN-S or TT), the conductor shall be not less than half the CSA of the earthing conductor for the installation, with a minimum of 6mm² copper. The bonding must be continuous, securely fixed, and connected with BS EN 61238-1 compliant clamps (typically labelled "Safety Electrical Connection — Do Not Remove").

Common bonding failures include: clamps that have been removed during plumbing work and not refitted, bonding bypassed by plastic pipe sections (where a plumber replaces a section of copper with plastic without reinstating the bond), corroded or loose clamps, and undersized conductors (for example, 4mm² earth wire used as a bonding conductor).

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Most modern UK domestic properties are supplied with a PME (Protective Multiple Earthing) system, technically known as TN-C-S earthing. In this system, the DNO combines the neutral and earth conductors into a single PEN (Protective Earth Neutral) conductor in the supply cable. At the property, the DNO provides an earth terminal by connecting it to the neutral.

This works well under normal conditions. But if the PEN conductor develops a high-resistance joint or breaks entirely (a "lost neutral" or "broken PEN" fault), the consequences can be dangerous:

This is the reason BS 7671 has specific requirements for locations with increased risk — for example, bathroom supplementary bonding (Regulation 701.415.2) and restrictions on PME earthing for certain special installations. It is also why marina installations and caravan sites often use TT earthing instead of TN-C-S.

If you suspect a broken PEN conductor, measure the voltage between the incoming water pipe (before the bonding connection) and a known earth reference (for example, an earth rod). If the voltage fluctuates and is more than a few volts, contact the DNO immediately.

If you or someone in the property receives an electric shock from a tap, follow these steps immediately:

Never ignore a shock from a tap, even if it is mild. The fault will not fix itself and is likely to get worse. What starts as a tingle can become a life-threatening shock as the insulation deteriorates further.

When called to investigate a shock from a tap or pipework, follow a systematic approach to identify the source. The fault could be on the property installation, a connected appliance, or the DNO supply.

Always carry out safe isolation before working on any circuit. When testing near water and metalwork, use GS38-compliant test leads with fused probes, and take particular care with wet surfaces.

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Once the immediate fault has been fixed, there are steps to prevent a recurrence:

For electricians, every call-out for a shock from metalwork should result in a thorough check of the bonding and RCD protection across the entire installation — not just the specific fault that caused the call. Use Elec-Mate's EICR app to record your findings and issue a certificate if a periodic inspection is warranted.