In the event of heavy rain or thunderstorms, the proportion of filtered water is smaller. However, heavy thunderstorms only account for a small proportion of the total annual rainfall.
As a result, the WISY rainwater filters receive an annual average of approx. Filter 90% of the total rainfall and direct it towards the cistern and use 10% to continuously rinse the filter and keep it clean. This residual water volume automatically transports the dirt into the sewer.