Water slide is a type of slide or tube designed for warm-weather or indoor recreational uses, typically with water pumped to its top and flows along its surface, although some may simply be wet. A person can sit directly on the slide, or on a raft or tube designed to be used with the slide, and slide to the bottom via gravity. The water reduces friction so sliders can travel down the slide very quickly. Water slides run into a swimming pool (often called a plunge pool) at the end. Some, however, have long, flat and straight sections at the bottom with a few inches of standing water, frictional material, or rollers attached to the slide designed to slow the sliders and allow them to safely exit the slide.

Water slides are popular at water parks, such as the Wet 'n Wild parks in the United States or Sandcastle Waterworld at Blackpool in the United Kingdom. They are great alternatives to those who don't like such intense rides at other amusement parks. If the slides empty into a pool, the pool is usually designed only to catch sliders who must exit the pool immediately after coming to a stop, to prevent sliders entering the pool at high speed from striking other swimmers. These plunge pools are usually quickly cleared by other swimmers to avoid injury. Smaller water slides may be found at swimming pools in water parks, private locations and community recreation centers where larger "thrill" slides are absent.

In some countries, they are more commonly referred to flumes, water chutes, or hydro-slides.