Water usually leaks under a sink because a drain nut has loosened, a supply hose is wearing out, a shutoff valve is leaking at its stem, a seal inside the faucet has failed, or a dishwasher or disposal connection is dripping. Whether the leak happens all the time or only when the sink is used tells you which side of the plumbing to check.
Empty the Cabinet and Dry It
Take everything out from under the sink and wipe all the pipes and the cabinet floor dry. Lay a dry paper towel on the bottom. Now you have a clean slate to see where new water comes from.
Test the Drain Side
Fill the sink partway and let it drain while you watch. Drips that appear only now point to the drain: the curved trap, the slip nuts that hold it together, or the seal where the drain basket meets the sink. Plastic nuts can sometimes be hand-tightened, but overtightening can crack them.
Test the Supply Side
With the sink empty and the faucet off, watch the hoses and valves for a few minutes. Drips here mean the supply side is leaking. Braided hoses can fray and crack with age, and valves can weep around the handle. Because these lines are always under pressure, leaks on this side tend to get worse.
Check the Faucet and Appliances
Water that collects at the back of the cabinet may run down from a worn seal at the faucet base. In kitchens, check the dishwasher drain hose and the disposal for wet spots.
A soft or swollen cabinet floor means the leak has been going for a while. Close the shutoff valves until it is repaired.
If tightening does not stop it, the dripping connection can be repaired or replaced. Old supply hoses and valves are easy to replace during periodic sink and faucet maintenance. Call JPR Plumbing at (833) 603-1840.