There is a multitude of elements that can block an outdoor drain. These drains are far more susceptible to natural debris like trees, shrubs, dirt and leaves, which is why regular garden maintenance is essential. Sometimes, however, you cannot see the problem, as tree roots grow underneath the earth and search for water which will lead them straight to your drains. Throughout the wet season, heavy rainfall can also cause water build-up and an overflow of rainwater in gutters and downpipes. Your pipes may not be able to handle this much water, and it can cause issues.