Downpipes need to be able to handle the amount of rain and the speed at which it falls. ... This will ensure safe disposal of rain, to avoid damage to both your property and the neighbouring properties. Poor rainwater management systems can cause bigger problems too, such as flooding.
Downpipes carry rainwater from the roof of your house into the stormwater network. They should not enter the drain that is used for wastewater from inside your house (e.g. the kitchen, laundry, toilet).