A blockage is when your drain becomes clogged and the water cannot flow through. A blockage can happen for many reasons, but it is most commonly caused by hair or other debris that has fallen down the drains. There are some steps you can take to prevent a blockage from happening. One of them is to make sure you are not pouring cooking oil, grease, or fat down the drain because they will clog your pipes. Another one of these steps is to make sure that you don't pour any kind of food down the drain because it will rot and cause a blockage over time.