A slow drip beneath a sink can damage cabinet flooring before it becomes obvious. Inspecting the shutoff valves and nearby connections helps identify whether the moisture comes from the valve, supply line, or faucet connection.
Dry and observe
Wipe the pipes and valve dry, then place a clean cloth beneath each joint. Open the cabinet doors and observe after the water has been used.
Check the valve body
Look around the stem, compression nut, and supply connection. Do not force a stiff valve; an old valve may fail when turned.
Protect the cabinet
Keep a shallow tray or absorbent pad beneath the connection while monitoring. If water increases or the cabinet base is soft, shut off the main supply and arrange service.
Record the source
Take a photo of the wet point and note whether it occurs only when the faucet runs. This helps a plumber repair the correct fitting.