Venta Airwasher 6001436 Water Treatment Additive, 35 OzThe Venta Water Treatment Additive (WTA) is designed for the Venta Airwasher models to maintain hygienic conditions in the lower housing and to improve the evaporation process. It creates a sheeting action on the disks with the effect of maximizing the amount of surface area. It helps prevent calcium and lime build up and helps to keep the water more anti bacterial. Contains 35 Fl. Oz (sufficient for approx. 5 months months). Recommended usage: one