Several issues may cause poor water pressure. For example, there may be a clog in the showerhead, or you may have a low flow model. If it's clogged, it's likely due to mineral buildup. If the faucet is a single handle type, the internal mixing valve may need a replacement. Another common cause is a faulty water pressure regulator. There are many valves located throughout your plumbing system. If one of them is closed, you may experience a change in your water pressure. If you experience a change in water pressure only when you use hot water, your water heater may be to blame. Additionally, if your home has old pipes, they may corrode and leak, leading to water pressure issues.