When the gutters become clogged, the water does not drain through the downpipes as it should. Instead, it overflows over the front of the gutter or over the back of the gutter. When the water overflows over the front of the gutter, it is easy to notice; it usually erodes the soil below the leaking area and begins making black marks on the side of your home/building from the dirty water inside the gutter continually leaking. If the water in the gutter starts overflowing over the back of the gutter, it can leak inside your home, potentially creating mould. In addition, if there are fascia boards/rafters behind the gutter, these will begin to rot.