So, you have low water pressure..What does this mean to you and what kind of effects it has on your plumbing. Low water pressure can be caused by many things. Simple problems like the shut-off valve being closed or a faucet being blocked can cause low water pressure. More serious issues like plumbing blockages or water leaks decrease water pressure, too. Don't wait on issues like these..Call your plumber if you have any questions regarding low water pressure.