Find the source
Dry everything with a towel. Place dry paper towels under each fitting. Run the water for 30 seconds, then look:
- Drips from the P-trap (the curvy pipe) — usually a loose slip nut. Hand-tighten, then ⅛ turn with channel-lock pliers.
- Drips from a braided supply line — these fail after 8–10 years. Replace both hot and cold while you're under there. ~$10 each at any Canadian hardware store.
- Drips from the faucet base above — that's water running down. The faucet needs new cartridges or a reseal.
- Wet only when the dishwasher runs — check the dishwasher drain hose connection.
Quick wins
- Tighten slip nuts by hand first. If still leaking, snug ⅛ turn with pliers. Over-tightening cracks the plastic.
- Replace the cheap rubber slip-joint washer (~$2) before assuming the trap is broken.
Call a plumber
- Galvanized supply lines (silver, threaded) — these are 50+ years old and crumble when touched.
- Wet drywall in a wall cavity — that's a hidden leak, not under-sink.