Backwashing

Backwash is the backwards flow of air or water. Backwash can be created naturally by waves rebounding off a beach or other obstacle. It is created by  propulsion devices such as an oar or engine. Unlike a slipstream, a backwash is harder to travel through than normal, and in sports such as rowing avoiding a competitor's backwash is important.
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spalare în contracurent; spalare inversa

In a wastewater or water treatment facility, the flow of clean water in a direction opposite (upward) to the normal flow of raw water through rapid sand filters in order to clean them.

Reversing the fluid flow through a filter to clean out sediment that has clogged the filter or reduced its efficiency. Back washing is done on closed system filters and on open-bed, gravity filters.

Reversing the flow of water back through the filter media to remove entrapped solids.