There are four primary reasons a faucet may be running slowly: A low-flow faucet aerator is installed, the aerator screen is clogged, the shut-off valves are not fully opened, or the faucet supply tubes are either crimped or crushed. Most of these problems can easily be checked and fixed.
The most likely reason for a faucet running slowly is that the shut-off valves have been bumped partially closed by something underneath the sink. Both valves can be found beneath the sink and should be turned counter-clockwise as far as they can go to ensure they are completely open.
If the water still runs slow after checking that the valves are completely open, the aerator should be checked. The aerator is the part attached to the end of the faucet. The aerator can usually be unscrewed by hand. If doing so is not possible, a towel or rag can be wrapped around the aerator to protect the metalwork, and the aerator then unscrewed with a pair of pliers.
Low-flow aerators are often installed onto faucet spouts to save on water consumption by reducing the water's flow. If this is the issue, there is likely a plastic disk inside the aerator. This disk cannot be removed and the entire aerator must be replaced.
The hot water tap running slowly may be a result of sediment building up inside the faucet and aerator. If this is the problem, a visible build up on the inside of the aerator is usually visible. The build-up should be gently scraped away and the aerator rinsed. Alternating between running the hot and cold water until the water runs clear may help. The aerator then should be replaced.
If the shut-off valves are completely open and there is no issue with the aerator, the water supply tubes beneath the sink need checking. The tubes should not crimped or compacted. If they look fine, the shut-off valves should be turned and the tubes disconnected. The ends of the supply tubes need to be put into buckets, and valves opened one at a time to ensure there is no blockage. If the water flows freely, there is a deeper issue with the faucet. If the water does not run freely, there is a further issue with the supply tubes.