What is rainwater harvesting?

We see a lot of rain here in the UK and, when it comes to growing fruit and veg, rainwater can help crops thrive. To easily get rainwater to these crops, gardeners will use rainwater harvesting.

Using this system, rainwater that would usually flow away down drains is collected and stored for future use. Gardeners will then plan how they want to distribute the collected water around their crops.  

If you would like find out how to harvest rainwater and set up a harvesting system that can be used in your polytunnel, follow our guide for some top tips to make your crops flourish.   

How to use rainwater harvesting

Before you get started, it’s worth taking some time to decide how you would like to use rainwater harvesting in your polytunnel. Doing this will give you an idea of how to maximise the potential for the water you collect.  

Plan it out

If you have been growing crops in your polytunnel for a while, you will have already invested lots of time in setting up your polytunnel in a way that works for you. Whether you have a 6ft one or something bigger, you will have a section for your tomatoes and will have created space to allow for your onions.

When it comes to using harvested rainwater, it’s worth noting the crops that will need more water than others. The aim is to ensure that the water reaches as many plants as possible, so sharing it out between your crops will help to get the optimum nutrients from the rainwater to them.

Make some updates

Like all gardening systems, rainwater harvesting requires some trial and error. Keeping this in mind before you set up your system and begin the harvesting process will be beneficial for both you and your crops.

When planning it all out, factor in time to make any necessary adjustments. Having some time set aside for any updates you would like to make before you begin harvesting is a great way to manage things when you set up your system.

For example, once you begin, you may find that one plant enjoys more rainwater than another. By slotting in the time early on to make some changes to the way you distribute your harvested rainwater, you can ensure your plants will be getting the nutrients that they need without impacting on the rest of the gardening process.

What is rainwater harvestingSet up your system

Setting up your rainwater harvesting system in your polytunnel is made easy with the right accessories. To begin, you will need robust polytunnel gutters. If you don’t have any fitted to your polytunnel already, now is a great time to invest in some to help you retrieve that all-important, nutrient-rich rainwater.

A water butt is the most common receptacle for rainwater. Place your water butt at the end of your gutter and the rainwater will run off and into the butt. From there, you can funnel the collected water and apply it to your crops. You can opt to position your gutters so the water runs into one butt or you can invest in two water butts to sit at either end of your polytunnel.

Why harvest rainwater?

There are plenty of reasons to switch your current irrigation system to rainwater harvesting. Here are some of them:


We’re guaranteed to get some rainfall in the UK. Therefore, choosing to reuse rainwater to hydrate your crops is a sustainable way of repurposing water that would usually be destined for a drain.

In addition, by opting to harvest rainwater collected in a water butt, you are choosing this over the alternative irrigation method of using a mains supply, which may use a lot of energy and which may not be available during regional water restrictions or on some allotments.  


Rainwater contains plenty of nutrients for your crops, making it an excellent choice for helping them to flourish. In addition, unlike tap water, which has been treated to make it suitable for drinking, rainwater is free of any added chemicals.


Using water from a mains supply to irrigate your crops can be expensive, especially if you’re trying to focus on growing several crops at once in time for harvest. Rainwater is a free option that can do wonders for the fruit and veg you grow. Once you have invested in high-quality gutters and some water butts, you won’t have to pay out again.  

Repurposing rainwater

Whether you’re new to growing in your polytunnel and want to set up a sustainable irrigation system or you’re a gardening pro who is seeking a cost-effective alternative to your current set-up, then rainwater harvesting is the perfect solution. To find out more about the polytunnel accessories you will need to begin rainwater harvesting, see what’s on offer here.

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