Wall jets in swimming pools work as part of the internal filtration and circulation system, pushing the filtered water back into the pool due to pressure from the impeller. As the water enters the system through suction from the pool pump, the filters remove small and large debris to keep the water clean.
Wall jets are the final component in a pool's filtration system, which begins with a series of skimmer boxes around the edges of the pool and a single main draining point. The pool's pump filter pulls the water in through the drain, collecting the additional water entering the system through the skimmers, and forces it past the first filter to remove large objects such as twigs or bugs. This process creates negative pressure in the inner components, causing the water to move through the system and into the impeller, where it experiences a second filtering.
Once the water moves through all the filters, it enters a return line that connects to a series of holes just below the surface level. The force built up by the filtration process pushes the water out of the holes, creating a water jet effect that pushes the cleaned water back into the pool. Some pool systems also incorporate additional treatment options after the final filtering stage. It is also common in more expensive systems to include options to head the water before it reaches the jets.