When a cold water system is being decommissioned, which action should be performed first to ensure safety?

• A. Isolate and reduce the system pressure
• B. Bleed air from the highest point
• C. Open all taps to relieve pressure
• D. Seal the cistern

Answer: (A)

The first thing to do when decommissioning a cold water system is to stop the source of water and bring the pressure down. By isolating the system—the shutoff and any local valves—you cut off any future flow, so the network isn’t pressurized while you work. Depressurizing makes it safe to handle pipes and fittings, greatly reducing the risk of water spurting, leaks, or water hammer if components are disturbed. Bleeding air from the highest point should come after isolation to remove trapped pockets, not as the initial step. Opening all taps while the supply is still connected will just keep water moving and pressure present. Sealing the cistern isn’t addressing the safety issue of pressurized water and can trap water and contaminants. So isolating the supply to reduce pressure is the safest, most effective first action.