Nowadays some many people take for granted the fact that when they turn the knob on the faucet they know water will come out. However, they have no idea how the plumbing system in their home or apartment works. Lets discuss a few main functions of the plumbing system.
Water Supply. How does your house even receive running water. Whether you're hooked up to city water supply or a well water system, the house is supplied water from 1 single water line into the house. Once the water line enters the house it diverts to several channels supplying water to every water fixture in the house. The main water line typically enters the house near the hot water tank and make it's first split, and the hot water line leads into the tank to heat up and the cold water line diverts to the rest of the house. Once the water has passed through or around the water heater it is supplied to every sink, shower, bathtub, toilet, appliances, etc in the house. From there each fixture in your house has a simple valve that controls the water from there. When you turn the sink faucet or the shower handle, it opens the valve and allows water to flow. In order to keep water "on demand" at each plumbing fixture, the water supply lines must stay full and pressurized with water. Due to this, there is always a risk that plumbing fitting or coupling could leak at any time. Because of this, you should stay diligent to watch out for leaking in walls or under houses, as well as lower water pressure. These are signs of plumbing leaks and should be addressed immediately.
Drain Lines. Once the water has been supplied to your sink, shower, bathtub, toilet, etc it then flows into the drain lines and subsequently into the sewer line and then into whatever sewer system you have at your house. It can either be a city sewer system or a septic sewer system. Depending on where you live and when your house was built there are several different drain line materials that you might have in your house. In the early 1900s in the United States, we were using clay pipes as drain lines. Clay pipes are durable and don't corrode very easily, but they are very heavy and difficult to transport and difficult to work with. Later, the common material of choice was Cast Iron, which is durable as well and slightly easier to transport and work with, but slightly more susceptible to corrosion over time. Also, like clay pipes, they can crack & break with shifting soil. They are both also susceptible to roots getting in around the joints. The most recent and most commonly used drain line material today is Plastic PVC pipe. PVC pipe is very light, very cheap, and very easy to transport and work with for plumbers. Joints can fit much tighter than cast iron or clay pipe so it's more resistant to roots getting into the sewer line. It's important to understand that no matter what material is used, every single sewer line & drain line has a shelf life and will eventually need to be repaired.
Staying on top of your plumbing system and consulting a professional plumber anytime you notice difference in performance is important in preventing any long term issues.