New Handwash Basin in a Food Prep Area
A small restaurant is adding a staff handwash basin in a prep area. The nearest supply is a 15 mm cold-water branch 3 m away that also feeds a vegetable washing sink through a flexible hose. The nearest drain is a 50 mm floor trap 2.5 m away. The basin will be used only for handwashing. The local code requires an air gap or an approved backflow preventer on the supply, a smooth impervious surface, and a trap with a 50 mm water seal. The owner wants to connect the basin drain directly into the floor trap and use a simple tap with a pull-out spray. The water pressure is 3.5 bar. You must advise on supply protection, drainage, and the risk of the spray hose.
1. Identify the backflow risks in the proposed installation and specify how the supply should be protected.
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The main risks are the pull-out spray on the handwash basin and the flexible hose on the vegetable sink. If the spray head can be dropped into the basin or sink, or if the hose can reach below the flood-level rim, contaminated water can be siphoned back into the supply when pressure drops. The tap outlet must have an air gap, with the outlet at least 25 mm above the overflow rim of the basin. A pull-out spray should have an integrated vacuum breaker or a hose-connection vacuum breaker, not just a plain check valve. The vegetable sink’s flexible hose is a separate risk and should be protected by an approved backflow preventer suitable for the hazard, or replaced by a fixed outlet with an air gap. At 3.5 bar the pressure is adequate, but it does not remove the backflow risk.
2. Advise on the drainage arrangement, including the trap, vent, and connection to the floor trap.
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The handwash basin should have its own trap with a 50 mm water seal, and the trap should be accessible for cleaning. The drain should be vented to prevent siphonage; if the basin is close to the floor trap, a branch vent or an approved air admittance valve may be acceptable under local code. Connecting directly into the floor trap is not automatically wrong, but the floor trap must not be relied on as the basin trap, and the connection must not allow sewer gas or backup into the basin. In many food premises, handwash basins are discharged indirectly over a floor sink with an air gap, which is the safer arrangement. Do not connect the handwash basin to the kitchen grease interceptor; that interceptor serves grease-laden kitchen fixtures, not handwashing waste.
3. The owner says the spray hose is convenient and asks whether a simple non-return valve on the supply will be enough. How would you respond?
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A simple non-return valve is not sufficient protection for a hose-connected outlet. Non-return valves can foul, jam open, or be defeated by back pressure, and they are not an approved air gap. Explain that the code requires an air gap or an approved backflow preventer, and that the spray hose is a direct connection that can reach contaminated water. Offer a compliant alternative: a tap with an integral vacuum breaker and a spray head that cannot reach below the rim, or a fixed spout with an air gap. If the owner insists on the hose, fit a hose-connection vacuum breaker and check that the spray head hangs above the flood rim. Record the advice in writing, because the risk is a health inspection failure and possible contamination of the supply.