What is backwashing in pool maintenance?

Backwashing is a crucial process in pool maintenance that involves reversing the flow of water through a filter. This technique is employed to clear out accumulated debris, such as dirt, algae, and other contaminants that have been trapped in the filter media. Over time, filters can become clogged, which can reduce their efficiency and the overall cleanliness of the pool water. By backwashing, you effectively flush out these unwanted particles, allowing the filter to work more efficiently and ensuring that the pool water remains clean and clear.

The other choices do not accurately describe the process of backwashing. Changing pool water involves draining some or all of the water in a pool and replacing it with fresh water, which is not related to filter maintenance. Cleaning the pool surface refers to removing debris from the pool's floor and walls, which is a different aspect of pool care focused on physical cleanliness rather than filtration. Adding chemicals to the pool addresses water balance and sanitation, yet it does not pertain to the physical cleaning of the filter system itself. Thus, the definition provided in the correct answer captures the specific and critical function of backwashing in pool maintenance.