If your city hasn't decreased the water pressure to your building, a sudden drop may be caused by a failure in your water softening system. Specifically, the water softening resins inside it may be giving you more grief than the minerals they're supposed to block out.
What Is Water Softening Resin?
In order to soften water, or remove its mineral impurities, your system has to pass it through a special resin filter. This negatively charged resin releases sodium into the water and captures the positively charged calcium and magnesium particles as they go past. Once they reach the end of their 20-year lifespan, these resins can begin to break down into tiny, sand-like fragments, which may appear in your water and get stuck inside your fixtures.
Since it's generally regarded as a bad idea to continuously sandblast your home's plumbing from the inside, and you probably shouldn't consume resin fragments either, you'll need to have the softener repaired. Replacing the old resins with new ones and flushing out your pipes should only take a couple of hours. If the resins have been wearing down and accumulating for an extended period, you may need to have the softener professionally cleaned out.
What If The Resins Aren't The Problem?
Sometimes, pipes that have had hard water in them can experience a sudden drop in water pressure due to clogging. This happens when old mineral deposits become dislodged inside the pipes. The water carries them through your plumbing until they reach an outlet, which then becomes partially clogged. Common signs of this problem are showerheads and faucets that clog when nothing else does. Usually, opening up these fixtures will allow you to clean out the mineral buildup.
If the clog occurs inside a thin pipe, rather than a fixture, you may need a plumber to take the pipe out and remove it for you. You can usually tell this has happened if one part of the house has lower water pressure than the rest of the home. On the other hand, if you have a DIY spirit and own a drain snake, you can always flush out your home's water and clean the pipe out yourself. Be sure to avoid liquid drain cleaners, however, since their chemicals can't break down the mineral deposits, but can damage your pipes.
Sudden low water pressure can be a sign of damage to your softening system. If you've noticed some of your fixtures dribbling when they used to gush, it's a good idea to have a professional soft water company give your plumbing a checkup.