Cold Water Slow? Fix Low Water Pressure Under Your Sink
Having low water pressure from the cold water tap under your sink can be incredibly frustrating. Just when you need to fill up a glass or wash your hands, the water barely drips out. Low flow can make tasks take much longer and leave you with messy, wet countertops.
But don't panic - in most cases, low water pressure under the sink is an easily solvable issue. By methodically checking a few key areas and making a few adjustments, you can likely get your cold water flowing properly again without having to call in a plumber.
Check Your Main Shut Off Valve
The first thing to check when troubleshooting low water pressure under a sink is your home's main water shut off valve. This valve is typically located where the main water line comes into the house, either at the front of the home where city water connects, or near the well system.
Over time, debris can collect inside the valve, preventing it from opening fully. This reduces water flow for the entire house. Locate the main valve and turn the handle to ensure it moves freely and is wide open. While you have it open, check for any dirt or minerals that may have built up inside the valve chamber. Carefully clean out any debris so it cannot limit flow.
Inspect the Valve for Corrosion
A main water shut off valve, especially an older outdoor valve, can also corrode internally. Chunks of rust can break free inside the valve body, blocking water flow. Inspect closely for any visible corrosion inside the valve chamber when you have it opened up. If you see flaky rust, you may need to replace the main valve to restore full water pressure.
Keep in mind that if you have low water pressure from sinks all over the house - like showers, exterior hose bibs, etc - the issue is likely with your main water pressure coming into the home. Fixing the main valve should solve pressure issues under a specific sink.
Inspect Supply Lines Under the Sink
If low water pressure seems isolated to just the one kitchen or bathroom sink, the issue could be with the small supply lines and plumbing fittings directly under that sink. Take a flashlight and carefully inspect the water lines that feed both the hot and cold faucets.
Check for Blockages
Old galvanized steel pipes under a sink can become internally corroded over years of use. Mineral deposits from the water collect in any rough areas inside the pipes, gradually restricting flow. Visually inspect the cold water pipe for corrosion or uncommon bulges that may indicate a partial blockage.
If the old galvanized plumbing has become completely clogged with mineral buildup, replacement is likely your best option to restore full pressure. Consider upgrading to smooth copper pipes or flexible PEX tubing that is resistant to internal corrosion.
Watch for Kinks
The small space under a sink can also cause problems with stiff water supply tubes. Copper and PEX pipes are prone to getting kinked or bent at sharp angles as they snake around drain lines and under the countertop. Even a small kink can dramatically reduce water flow.
Carefully trace the cold water line from the supply valve up into the base of the faucet. Straighten out any sections that have an abrupt crimp or bend. Securing the line properly can help prevent future kinking.
Clean Out the Aerator
At the tip of nearly all modern faucets is a small aerator screen. This piece utilizes a fine mesh filter to remove sand, grit and other particles from the water as it leaves the faucet. But over time, this screen can get clogged with mineral scale, once again restricting flow.
Simply unscrew the aerator from the end of the faucet head and rinse out any debris caught in the screen. Make sure to flush the line for a few seconds afterward to clear any remaining grit in the line. Reinstall the clean aerator piece and check your water pressure.
Consider Replacing Old Aerators
If the aerator is heavily corroded or damaged, replacement may be necessary to restore full pressure. Newer sink aerators also employ water saving restrictions and specially designed flow channels. Upgrading to an new, high-efficiency aerator can boost your cold water pressure while still preventing splashing or excessive water use.
Make Sure Shut Off Valves Are Fully Open
Nearly all sinks have individual shut off valves controlling water flow to the hot and cold faucet lines. They typically look like small metal wheel handles located under the pipe joints behind the sink basin. If your cold water pressure is low, make sure the shut off is turned on all the way.
These valves can loosen or wiggle slightly over time, slowly shifting closed. Or the homeowner may have intentionally turned down the valve at some point for maintenance, then forgot to fully open it later. Cold water issues under one sink only can often be resolved by simply making sure both valves are wide open and the handles are parallel with the pipe.
Replace Faulty Shut Off Valves
Old galvanized steel shut off valves can also get stuck or refuse to fully open, causing occasional water flow problems. Try opening and closing the valve handle several times to break free any interior corrosion. Spray lubricant inside the valve body if the handle still won't turn freely.
Ultimately though, replacement with new 1/4 turn ball valves may be required. Modern shut off valves use smoother internal components to prevent obstruction and are simply more reliable in the long run.
Consider Replacing the Faucet
If your kitchen or bathroom faucet is 10+ years old, mineral scale and corrosion buildup within the faucet body could hamper your cold water pressure. Old faucet aerators and washers allow higher flow rates that can exacerbate pressure drops through built up pipes.
New high-efficiency faucets include flow restrictors and specially designed channels that focus water pressure to maximize flow even through corroded pipes. If you have galvanized supply lines filled with mineral deposits, upgrading to an newer faucet with better internal water channels can counteract some of that corrosion.
Look for Certified High Efficiency Ratings
When shopping for a new kitchen or bathroom faucet, look for the EPA's WaterSense certification. WaterSense taps have undergone rigorous independent testing to verify they achieve solid water pressure levels while using at least 20% less water than standard models.
When to Call a Plumber
In many cases, limited cold water flow under a sink can be quickly addressed with some DIY adjustments as discussed above. But if your flow issues persist even after a thorough inspection and troubleshooting, professional assistance may be warranted.
Signs that a plumber may be needed include flow problems in multiple areas of the home, visibly corroded and degraded pipes that require replacement, or complex setups where supply tubes are difficult to access. If queries persist despite your best efforts, don't continue struggling with low water pressure - call a professional.
Professional Diagnostics and Maintenance
A licensed plumber can run in-depth flow rate diagnostics to precisely locate obstructions. They can also use high pressure jetting equipment to clear out stubborn mineral deposits and corrosion inside pipes that resist DIY snaking attempts.
Professionals also have experience working in cramped sink base cabinets to splice in new shut off valves or replace troublesome galvanized supply tubes. Don't take chances trying to force stiff tubing into small spaces or alter complex valve arrangements on your own.
Don't let frustratingly low water pressure under your kitchen or bathroom sink continue causing headaches. Inspecting key connection points and clearing out obstructions can often get your cold water flowing properly again.
Focus first on the main water line coming into your home, then work downstream to supply tubes under the sink. Clean aerators, straighten kinked pipes, and make sure shut off valves are fully open. If simple DIY fixes don't solve your problems, seek professional assistance to replace worn plumbing components.
Take the time to properly diagnose flow issues instead of just coping with a slow dripping faucet. A little targeted troubleshooting can go a long way towards improving your experience in the kitchen or bath.