There are many factors that can affect water pressure. Low pressure can be the result of a solitary issue in a single component or a universal problem that is beginning to unfold in a specific location.
If a plumbing problem is localized, it's always best to attempt to diagnose the problem at the source, working outward to possible system failures only when no local issues can be found.
What Issues Can Affect a Faucet's Water Pressure?
Various parts of a faucet can restrict flow when they become clogged or corrupted, including:
The aerator is the small round attachment that is connected to the faucet's spout. Its function is to regulate water pressure by adding air to the natural flow of the water as it leaves the spout.
This is accomplished by forcing the water through a small wire mesh screen at the end of the aerator. Hard water or corroded supply pipes can cause the screen to become clogged over time, restricting the amount of water that can pass through the spout.
Use a pair of pliers to remove the aerator, turning it counterclockwise until it comes loose. While you can clean the aerator screen by soaking it in vinegar overnight to loosen mineral deposits, it's easier to spend a few dollars at a local home improvement store to buy a new one, preferably a low-flow aerator.
Installing a low-flow aerator to replace the old model will provide equal water pressure to a functional older style aerator while using less water. If there is still a water pressure issue after the aerator is replaced, the supply valves may be at fault.
The supply lines that bring water to your sink are interrupted by supply valves that can be shut off in cases of emergencies such as breaches of the supply hoses or broken faucets that won't shut off.
You must first determine if one of the valves has been partially closed through an accidental shove by an object placed under the sink for storage. When shutoff valves are fully open, their handles are parallel to the supply lines to which they are attached.
This configuration allows an easy visual inspection of the flow of water through the valve. If a valve handle is at a partial angle, the flow of water is restricted through the valve. However, if both valves are fully open, there may be internal damage that requires a valve replacement.
This is probably a task better suited for a plumbing services professional, who can also look for systemic causes for low water pressure if the valves are eventually determined to be fully operational.