Reënstok is a facade tank that replaces a downspout. Rainwater, stored in these buffer tanks, no longer goes directly to the sewers. Water is collected and stored for in situ recovery: watering balconies, gardens at the foot of the building. The use of rainwater is also possible, on each floor, to supply the toilets, the washing machine in addition to the public network. This buffer device also has another advantage: that of a regulator, by absorbing excess water in the event of a storm to prevent overflows from the treatment plants and by ensuring the flow necessary for the proper functioning of the sewers in dry periods. à supprimer Composed of modules, this tank is erected without height limit up to the roof. This system purges itself automatically in the event of severe frost.