Filtration installation for filtering the water of a water pool

A filtration installation for filtering water of a water pool (2), in particular of a swimming pool, arranged to be filled with water up to a predetermined water level (3), which installation comprises a filter vessel (4) separate from the water pool (2) and containing a filter bed (5), the filter vessel (4) being arranged to be installed next to the pool (2) with its filter bed (5) situated at least partially underneath said predetermined water level (3), with at least one inlet pipe (6) extending between the pool (2) and an upper portion (12) of the filter vessel (4) for conducting water from the pool (2) to the filter vessel (4) and with at least one return pipe (8) extending between a lower portion of the filter vessel (4) and the pool (2) for conducting filtered water having passed through the filter bed (5) to the pool (2), the installation further comprising a reversible pump (9) enabling to generate, in a backwashing state, an upward flow of water through the filter bed (5), and at least one drain pipe (11) arranged for removing the water pumped by the pump (9) in its backwashing state through the filter bed (5) into the upper portion (12) of the filter vessel (4), characterised in that the upper portion (12) of the filter vessel (4) is in liquid communication through said inlet pipe (6) with the water in the pool (2) so that water from the pool (2) can flow by gravity through the inlet pipe (6) into the filter vessel (4), the inlet pipe (6) is provided with a one-way valve (10) arranged to prevent a flow of water from the upper portion (12) of the filter vessel (4) into the pool (2), the drain pipe (11) is arranged upstream the filter bed (5) but downstream the one-way valve (10), and said reversible pump (9) is disposed downstream the drain pipe (11) so that the water pumped upwards through the filter bed (5) in the backwashing state of the pump (9) is removed through the drain pipe (11) whilst in the reversed filtering state of the pump (9), water is pumped out of the pool (2) to generate a flow of water from the pool (2) through the inlet pipe (6), the filter bed (5) and the return pipe (8) back to the pool (2).