The monthly check that prevents most of this
Two minutes, once a month, with a torch. It is the single most effective thing on this page.
Feel the shutoff valves where they meet the supply lines, and the connections at the faucet above.
Run your hand along the trap and each slip nut.
Look at the disposal — where it meets the sink, at the dishwasher inlet on its side, and underneath at the bottom of the housing.
Check the cabinet base itself. Swelling, discolouration, or a lifting edge means water has been there for a while, whether or not anything is wet today.
Look for white or green crust on fittings. That is mineral residue left by a leak that evaporates between visits — a leak you would otherwise never catch.
Worth knowing
Cabinet base damage is the giveaway that matters. A drip that dries between checks leaves no water but does leave a swollen or stained board. If the base is deteriorating, something has been leaking regardless of whether you can find it wet.
Supply lines and shutoffs
The highest-consequence failure under a sink, because supply lines are pressurised continuously — unlike a drain, which only carries water when something runs.
Braided stainless supply lines are the standard and they are not permanent. They have a service life, and the failure mode is a burst rather than a drip. If yours are old, or are plastic, replacing them is inexpensive and worth doing.
Shutoff valves seize. They sit untouched for a decade, and then on the day you urgently need to stop water, the handle will not move — or it turns and the valve weeps because the packing has dried out. Turn them off and on once a year.
High pressure shortens all of it. Above 80 psi, every connection under that sink is overstressed permanently. A gauge on an outdoor hose bib settles it — see high water pressure.
The ice maker line deserves specific mention. It is small, often plastic, frequently routed behind a heavy appliance nobody moves, and it fails quietly onto a floor you cannot see. Braided stainless is a worthwhile upgrade.
The disposal
Where it leaks determines whether it is a repair or the end of the unit.
From the top, at the sink flange — the seal has failed. Repairable: the unit comes down and the flange is re-sealed.
From the side — the dishwasher inlet or the discharge tube. Usually a gasket or a loose connection, and cheap.
From the bottom of the housing — the internal seal between the grinding chamber and the motor has gone, and water is reaching the motor. Not economically repairable, and an electrical hazard. Replace it.
For a disposal that hums or will not start, the fault is diagnosed by sound — covered in hum versus silence. For keeping one alive, the two habits that matter are cold water and letting it run a few seconds after the grinding stops: disposal care.
Drains, and the kitchen's particular problem
Kitchen drains block differently from bathroom ones. Bathrooms are hair; kitchens are fat.
Cooking fat goes down as a liquid and is solid twenty feet along the line, coating the pipe wall rather than passing through. Running hot water after it does not help — it relocates the problem further down where it is harder to reach.
Our hard water makes it worse: fats react with calcium and magnesium to form a deposit considerably harder and more adherent than grease alone. It is the same chemistry that makes commercial kitchens here need more frequent attention.
So the rule is simple and it is entirely about habit: cooled fat into a container and into the bin, greasy pans wiped with kitchen paper before washing, and cold water at the disposal.
If the sink is already slow, a plunger with the second basin blocked, then cleaning the trap, clears most of it — see clearing a drain properly. If more than one fixture in the house is affected, that is the main line, not the kitchen.
Faucets, filters and remodels
A dripping faucet is a cartridge or a washer, and where it drips from tells you which. Weak flow at the tap is usually a scaled aerator — soak it in vinegar before assuming anything about pressure. See fixing a leaking faucet.
Under-sink filters need their cartridges changed on volume rather than on the calendar, and carbon gives no visual warning when it is exhausted — it looks identical on its last day. If the taste returns, that is the indication. More in why filtered water still tastes of chlorine.
If you are remodelling, the plumbing decisions come earlier than most people expect. Moving a sink means moving the drain, and on a slab that means breaking concrete — which is often the difference between a straightforward refit and a much larger job. Establish that before the design is settled, not after.
It is also the cheapest moment to replace ageing shutoffs and supply lines, add an ice maker line properly, or fit a filter — while everything is accessible.