Why Does Heavy Rainfall Cause Blocked Drains?

If you live in the UK, you will know heavy rainfall can appear from nowhere and stick around for a while. At First Response Drainage, we notice that during and following these periods, there is an increase in the number of callouts we get. This is because rainfall produces an influx of drainage problems. Heavy rainfall can be responsible for blocked or broken drains and may even cause sewer backups. But how exactly does rainfall cause drainage issues?

heavy rainfall causing blocked drains

Excessive Amounts of Water

Drains are designed to cope with a certain volume of water, not the vast amounts of water that come with heavy rainfall. An older drainage system will particularly struggle to divert water away from the property, meaning that water can build up in the pipe. In turn, water will not correctly flow as it should, which may lead to a backup.

Debris Build-up

Your garden is likely to be covered in leaves, dirt, and sticks. Whilst they are harmless most of the time, heavy downpours can divert this debris into your drainage system, carrying it towards your drains and pipes. One such matter is inside your drainage system, it can cause a myriad of problems.

Debris can build up and cause a blockage, meaning that water is not able to flow through the system. When there is nowhere for the water to travel – just like when there is an excessive volume of water in your pipes– build-ups can cause sewer backups or burst pipes.


It is normal for small plants to grow in your drainage system. Although many people are not aware of it, such plants often grow from our own vegetable and seed disposal from the foods we eat. When we wash our plate in the sink, these seeds (e.g., tomato seeds) are washed down the drain and are given the chance to germinate in your drainage system. This is more likely to happen when there is a waste build-up, as the seeds can get stuck in your pipes rather than simply pass through.

Notably, small vegetation in your drainage system does not typically present a problem and can be easily fixed. If it rains heavily, however, plants can be pushed down your pipes and become stuck at one point. This can combine with other debris and cause a variety of drainage issues.

Tree Roots

Tree Roots often grow inside pipes in search of moisture, typically when there are small gaps in your pipework. When there is heavy rainfall, the speed and severity of this process can increase. Therefore, it is more likely that tree roots will lead to blocked and/or burst pipes.  

If you suspect any of the drainage issues above and need a professional touch, contact First Response Drainage today on 0800 043 4680. Our team of specialist engineers are on-hand to make sure that your drains stay in top condition