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Problems with water pressure are one of the more annoying things that can go wrong in a house. Showers become less satisfying and dishes are even more of a chore than usual. A lot of homeowners live with these and many other water problems, simply because they aren't aware of how to fix them (or prevent them in the first place). There are, however, many options available to change your water pressure from bad to "super-bad".
Urban Water Pressure
Most people get their water from a municipal water company. In the main lines underground, the water pressure is very high. Due to friction, this water loses its pressure between the main line and your home. It loses still more pressure between where it enters the home and the faucet it comes out of. The smaller the space is for the water to move through, the more friction there will be. If water has low pressure when it comes out of a faucet, it means that somewhere between the main line and your sink, the water is experiencing too much friction.
Sometimes, the excess friction is caused by pipes being too small in the first place. A pipe that is 1/2 inch in diameter causes significantly more friction than one that has a 3/4-inch or a full inch diameter. If your home is full of 1/2-inch pipes, replacing the ones that are easily accessible with 3/4-inch pipe will make a noticeable difference. Paying a professional to come in and replace all the plumbing with 3/4-inch pipe will make an enormous difference. People building a new home can upgrade from 1/2-inch pipe to 3/4-inch pipe for a relatively low price and save a lot of hassle in the long run.
Blockage Might be the Problem
Low water pressure can also be caused by blockages or chemical buildup in pipes. Water leaves small mineral deposits (often calcium) as it travels through plumbing. If enough of these deposits stick to the inside of the pipe, they reduce the diameter through which the water can flow (which in turn increases the friction, and so on). Since mineral buildup large enough to affect flow can easily be seen, examining a sample section of pipe from a fixture where the water pressure is low can identify this problem. Chemicals can be used to break down and flush out mineral buildup in these cases.