Have you noticed a leak under your sink? Is water pooling in the sink cabinet or on the floor? Unsure where it's coming from? There are usually three key causes of an under-sink leak. Before you check for these, it’s a good idea to remove any items from under the sink so you get a clear view of what's going on. A torch may also help.
1. A leak in the pressurised water hose
It will be apparent if this is the case: you'll see water spraying out constantly.
2. A drain line/waste pipe leak
If this is the cause of the leak, you'll only see water come out when the tap is on.
3. Drain seal/gasket leak
If either of the above two aren't the culprit, there could be a leak in the drain seal or gasket. Fill your sink and let the water drain away - if you see water escape, this is the cause.
With a little DIY and some understanding of sink plumbing, you may be able to avoid the cost of a plumber by fixing the issue yourself.
This pipe takes water to your tap. Connections and valves are usually where you'll see any leak. Often to blame are compression fittings around shut-off valves. Use a hand wrench to keep the valve in place, then tighten the compression nut with your hand.
If this isn't where the problem is coming from, it could be the connection between the tap and the pipe. These are troublesome to access. A pair of adjustable pliers will be invaluable in tackling the issue.
Over time, connections or washers can corrode or wear away. They may also loosen. Tighten compression nuts and connections. If this doesn’t solve it, a blockage could be causing the leak. Use a plunger to remove any detritus. If this fails to work, you may need to clean your P-trap (or U-trap or S-trap) or replace the washer. Use PTFE tape when you re-install to eliminate the chances of further leaks. Be sure to hand-tighten rather than use a wrench/grip, as the latter may crack the connection or make it difficult to remove next time.
If you find the compression nuts on your P-trap are difficult to turn, they may well have suffered corrosion.
In some cases the trap may need to be replaced. You can buy a new one from a plumbing or DIY store. If in doubt hire a plumber.
This is one of the easiest issues to fix. Unscrew the sink drain gasket, remove any grime and old putty, replace the washer if necessary, then add some new putty and re-install. In some cases the sink drain seal may need to be replaced completely. Again, you can purchase the entire part from a DIY/plumbing store, or hire a plumber to complete the task.
If you need a new washer and don’t have one to hand, you can use PTFE tape instead - although a new washer would work best.