What is a Wet Riser?

In buildings where speed and water pressure are critical to firefighting, a wet riser system provides an essential line of defence.

If you’re responsible for a tall building, it’s important to know what a wet riser is, how it differs from a dry riser, and when it’s required.

Wet risers are fixed firefighting systems designed to supply water instantly to multiple floors.

They’re part of the building’s fire protection infrastructure and are commonly found in taller commercial and residential buildings.

What Does a Wet Riser Do?

A wet riser is a permanently charged vertical pipework system filled with water under pressure.

It provides ready-to-use water outlets—known as landing valves—on each floor so firefighters can quickly connect hoses and begin tackling a fire without having to run hose lines from outside the building.

The system includes:

• A dedicated water supply, often a tank with a minimum volume based on the building’s height and usage
• Booster pumps to maintain constant water pressure throughout the system
• Landing valves within fire-rated cabinets on each level
• A fire brigade inlet at ground level, allowing additional water to be pumped into the system during a major incident

Wet risers ensure that water is immediately available wherever it’s needed, saving critical minutes and reducing fire spread in tall buildings.

Where Are Wet Risers Required?

In the UK, wet risers are required in buildings that exceed 60 metres in height.

This is because dry risers become impractical at these heights—water pressure from ground-level pumping becomes insufficient to reach upper floors quickly and reliably.

You’re most likely to find wet risers in:

• High-rise residential tower blocks
• Hotels and office towers over 18–20 storeys
• Hospitals or healthcare buildings with significant vertical rise
• Commercial premises with critical fire safety requirements

For buildings between 18 metres and 60 metres, dry risers are usually sufficient. In some cases, hybrid solutions or alternative fire strategies are used, depending on the building’s design and risk profile.

What Standards Apply to Wet Risers?

Wet risers in the UK must be designed, installed, and maintained in accordance with BS 9990:2015 – Non-automatic fire-fighting systems in buildings. This standard sets out all the technical requirements for:

• Minimum flow rates and water pressure
• System pipe sizing (usually 100mm internal diameter)
• Tank capacity (typically 45,000 litres minimum)
• Pump performance and redundancy
• Inlet/outlet design and access requirements
• Routine inspection, maintenance, and testing procedures

Other applicable standards and guidance include:

• BS EN 14384: Performance and safety requirements for wet riser outlets
• BS 5041 series: Covering fire hydrant and valve performance
• BS EN 12845 if the wet riser is integrated into a sprinkler system
• Approved Document B (Building Regulations) and relevant fire strategy documents

Maintenance and Testing Requirements

Because a wet riser is pressurised and filled with water, it must be regularly tested and maintained to avoid corrosion, leakage, or system failure.

Under BS 9990:

• A visual inspection should be carried out every 6 months, checking the condition of valves, cabinets, locks, signage, and accessibility.
• An annual full wet test should be carried out by a competent person, which includes:
  • Testing landing valves for correct operation
  • Measuring flow and pressure at each outlet
  • Inspecting the pump performance and water storage tanks
  • Ensuring correct function of alarms, isolation valves, and drain points

Records of all inspections must be kept for compliance under the Regulatory Reform (Fire Safety) Order 2005.

Wet Risers vs. Dry Risers

To recap the difference:

• Wet Risers: Permanently charged with water, used in buildings over 60 metres
• Dry Risers: Empty pipes that are filled by the fire brigade on arrival, used in buildings 18–60 metres

Each system has its place, and the right solution depends on building height, access, and risk.

How ESI Can Help

At ESI: Electrical Safety Inspections, we support building owners, landlords, and facilities managers across Farnborough, Camberley, Reading, Guildford, and the wider Hampshire, Surrey, and Berkshire area to stay on top of all fire safety systems—including wet risers.

We can:

• Carry out 6-monthly and annual wet riser testing to BS 9990
• Provide remedial works for faulty valves, pumps, or tanks
• Support compliance as part of your wider fire risk assessment
• Liaise with fire authorities and insurers for peace of mind

If you manage or own a high-rise building, it’s essential to ensure your wet riser is fully operational, correctly maintained, and legally compliant.

Get in touch with the ESI team today—we’ll help you get it right and keep everyone safe.