It sounds like you may have a problem with the pipes in your house. You can only get water flow if the inside diameter of the pipe is large enough to supply water to the lower fixtures and the upper fixtures. Water will always take the path of least resistance, unless there is enough volume and pressure to overcome the height and the number of openings. If your pressure or volume is low, whenever you open a faucet on a lower level, it will come out at only that location. The way to find out, is to measure the volume at the lowest opening. In a bathtub or laundry tub open a faucet on the hot side only and let it run into a 5 gallon bucket. If the bucket fills up in 5 seconds you have plenty of water pressure and volume. If the bucket fills up in 20 seconds, that's not very good pressure. Now repeat this on the upper floor with the lower level faucet closed. Then with the lower faucet open. If you find you are over 20 seconds. You may have galvanized pipes that have become so corroded there is no longer any flow. The flow is typically reduced because calcium and minerals build up on the inside of the pipe and block the flow like little dams.

Now if you don't have galvanized pipes, you may have a valve shut off someplace. If its the whole house thats low, it may be the main valve or the water supply into the house.

Good Luck

Raymond VinZant Plumbing Prof.