text: how does water pressure change? can somone please tell me how this happens? i would like to know how water pressure gets higher and lower. also the reason why this happenes... any help is greatly apperciated it... at your home, a water utility supply line into your home is typically only 1 inch in diameter.  this 1 inch pipe is split multiple time to route water to every watter connection in your home i.e toilet, shower, sink, outside faucet.  each of these connections is typically only 1/2 inch...so the more open lines a home has the lower the pressure will be, as the incoming pressure from the water company is held fairly constant.