What Size Water Butt Do I Need? A UK Guide to Choosing the Right Water Butt for Your Garden
If you’re thinking about installing a water butt, one of the first questions you’re likely to ask is:
“What size water butt do I actually need?”
And it’s a good question.
Choose one that’s too small and you may find yourself running out of stored rainwater just when your garden needs it most. Choose one that’s unnecessarily large and you could be taking up valuable garden space without making the most of the extra capacity.
The good news is that choosing the right water butt size doesn’t have to be complicated.
The ideal capacity depends on a few simple things: the size of your roof, the amount of rainwater you can collect, the size of your garden and how much water you use.
In this guide, we’ll explain the different water butt sizes, how much rainwater you could collect and which size could work best for your garden.
And if your water requirements change over time, we’ll also look at why a modular water butt system could be a smarter solution than simply buying the biggest tank you can fit.
Quick answer: what size water butt should I buy?
For many UK gardens, a water butt between 100 and 200 litres can be a useful starting point. With Rainwater Terrace water butts, our kits are modular so you can start small and increase as required. Our water butt connector kits makes this easy.
However, there isn't one perfect size for every garden.
A small patio garden with a few pots might only need around 67–134 litres of storage, while a larger garden with lawns, borders, hanging baskets, containers and vegetable beds could make good use of 200 litres, 268 litres or even 400 litres of rainwater storage.
The important thing is to think about how much water your garden actually needs, rather than simply choosing the largest water butt available.
At Rainwater Terrace, our modular system starts with individual 67 litre units and can be built into larger configurations, including 134 litre, 200 litre, 268 litre and 400 litre systems. This means you can choose a configuration to suit your garden rather than being restricted to one fixed-size tank.
What determines the size of water butt you need?
There are four main things to consider.
1. The size of your roof
Your roof is effectively the collection area for your rainwater.
The larger the roof area connected to your downpipe, the more rainwater you potentially have available to collect.
This means someone with a relatively small garden could still collect a surprising amount of rainwater if their water butt is connected to a large roof area.
2. The size of your garden
Think about how much watering you actually do.
Do you have:
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Lots of hanging baskets?
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Pots and containers?
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Flower borders?
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A vegetable garden?
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A greenhouse?
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A lawn?
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Newly planted shrubs?
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Fruit trees?
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Raised beds?
The more plants you have, the more useful stored rainwater becomes.
3. How often you water
A garden that is watered occasionally will require considerably less stored water than a garden containing dozens of containers and thirsty plants.
If you enjoy growing tomatoes, peppers, herbs, flowers and vegetables, having more rainwater storage available can make a noticeable difference during dry periods.
4. How much space you have available
This is one of the most overlooked considerations.
A water butt needs to fit somewhere practical.
You might have a large roof and plenty of watering requirements, but if you only have a narrow patio beside your house, a large traditional tank may not be the most practical solution.
This is where the shape and design of your water storage system matter just as much as its capacity.
Water butt sizes explained
Here's a simple guide to help you decide.
| Water butt capacity | Best suited to |
|---|---|
| 67 litres | Small patios, balconies, courtyards and smaller watering requirements |
| 134 litres | Smaller to average gardens, containers and flower borders |
| 200 litres | Average family gardens and regular garden watering |
| 268 litres | Larger gardens and gardeners with greater watering needs |
| 400 litres | Larger gardens, extensive planting, greenhouses and vegetable growing |
These aren't strict rules. A 67 litre water butt can be extremely useful in the right garden, while someone with a small garden may still want 200 litres or more if they grow lots of plants.
The important thing is to match capacity with usage.
Is a 100 litre water butt enough?
For some gardens, yes.
A water butt around this size can be a good starting point if you have a small garden, patio or a relatively modest number of plants.
However, remember that stored rainwater can disappear surprisingly quickly during warm weather.
Watering containers, hanging baskets and vegetable plants can use several watering cans of water at a time.
That's why it can be worth looking beyond the smallest possible water butt if you have the space.
A slightly larger system gives you more of a reserve when rainfall stops.
Is a 200 litre water butt enough for a garden?
For many households, 200 litres is an excellent middle ground.
It's large enough to provide a useful reserve of rainwater without requiring the footprint of a very large traditional tank.
A 200 litre system can be particularly useful for gardens with:
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Flower borders
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Pots and containers
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Hanging baskets
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Vegetable beds
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A greenhouse
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Young plants and newly planted shrubs
The Rainwater Terrace 200 litre system is a three-tier configuration designed to make use of vertical garden space while incorporating planters into the system.
That means your water storage doesn't simply have to occupy garden space it can become part of the planting scheme too.
What size water butt do I need for a large garden?
If you have a larger garden, 268 litres or 400 litres can make more sense.
A larger capacity gives you the ability to store more water following periods of rainfall, giving you a bigger reserve when the weather turns dry.
This can be particularly useful if you have:
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Large flower borders
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Lots of containers
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A greenhouse
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A vegetable garden
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Fruit trees
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Newly planted hedges
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Multiple areas that need regular watering
However, there is another option that is often overlooked.
You don't necessarily need one enormous water tank.
Instead, you can use multiple connected water butts.
Can I have more than one water butt?
Yes – and this can be a very practical solution.
Rather than buying one huge tank, multiple water butts can allow you to increase your rainwater storage capacity while making better use of the space available.
This is one of the reasons modular rainwater harvesting systems are becoming increasingly interesting for UK gardens.
Rainwater Terrace is built around individual 67 litre modules, which can be stacked vertically or connected horizontally. The system can therefore be configured to suit different spaces and expanded as your rainwater requirements grow.
For example, you could start with a smaller system and later add another unit when you realise just how much rainwater your garden uses.
That's very different from buying a fixed-size tank and discovering a year later that you need more storage.
What if I don't have much garden space?
This is where choosing the right shape of water butt becomes particularly important.
A traditional round water butt can take up a surprisingly large amount of floor space.
If your available space is beside a conservatory, greenhouse, fence or patio, a modular system can give you more flexibility.
Rainwater Terrace can be configured vertically when you want to maximise height, or horizontally when you have a longer but narrower area available. The 134 litre double configuration, for example, is designed to expand horizontally and can work well beside areas such as conservatories or greenhouses where blocking windows and light isn't desirable.
So when choosing a water butt, don't just ask:
“How many litres do I need?”
Also ask:
“Where am I going to put it?”
What size water butt is best for a vegetable garden?
If you grow vegetables, having a reliable supply of rainwater can be particularly useful.
Tomatoes, cucumbers, courgettes and other crops can need regular watering during dry weather.
If you're growing vegetables in raised beds, containers or a greenhouse, we'd generally suggest considering 200 litres or more, depending on the size of your growing area.
And there's another benefit to collecting rainwater.
Rainwater is naturally soft and is an excellent choice for watering many garden plants.
Instead of reaching for the hose every time your plants need a drink, you can use the water you've already collected from your roof.
What size water butt do I need for a greenhouse?
Greenhouses can be surprisingly thirsty places during warm weather.
Plants grown under cover don't receive natural rainfall directly, so all their water needs have to come from somewhere else.
If you have a greenhouse, consider positioning your water butt close to it or connecting it to a suitable downpipe or rainwater collection point.
A 200 litre system can be a good starting point, while larger greenhouses and intensive growing areas may benefit from 268 or 400 litres of storage.
The advantage of a modular system is that you don't have to perfectly predict your future watering requirements on day one.
You can increase your capacity later.
How much rainwater can a water butt collect?
This depends on your roof area and rainfall.
A useful way of thinking about it is:
Rainfall × roof area = potential rainwater collection
Even relatively modest rainfall can produce a substantial amount of water when it falls across a large roof.
For example, a 10mm rainfall event falling on a 50m² roof represents approximately 500 litres of rainwater before allowing for collection losses.
That doesn't mean a 500 litre tank will necessarily fill every time it rains the amount you actually collect depends on the roof area connected to the system, rainfall intensity, collection efficiency and how much storage capacity you have.
This is why having sufficient storage matters.
A small water butt may fill quickly during a rainy spell and then overflow, while a larger system can capture more of that rainfall for use later.
For more information, read our guide:
How Much Rainwater Can You Collect From a Water Butt?
Should I buy the biggest water butt I can afford?
Not necessarily.
It can be tempting to think:
“More storage must always be better.”
But the biggest tank isn't automatically the best solution.
You need to consider:
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Available space
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Roof collection area
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Garden size
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Watering requirements
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Accessibility
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Appearance
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Future expansion
A modular system can offer a useful compromise.
Instead of committing to one enormous tank, you can start with a sensible capacity and expand your storage if you find you need more.
Why a modular water butt could be the smarter choice
Traditional water butts are generally fixed-capacity products.
You buy the tank, find somewhere to put it and that's essentially the end of the decision.
Rainwater Terrace takes a different approach.
The system is built from 67 litre modular containers, allowing configurations to be changed and additional storage to be added.
Current Rainwater Terrace configurations include:
67 litres
A compact starting point for smaller spaces.
134 litres
A useful option for smaller and average gardens.
200 litres
A versatile choice for regular garden watering.
268 litres
More storage for gardeners with greater watering requirements.
400 litres
Designed for larger-scale rainwater collection and gardens with substantial watering needs.
This means you don't necessarily have to get your calculation perfect on day one.
Your rainwater storage can grow with your garden.
Why choose Rainwater Terrace instead of a traditional water butt?
Choosing the right capacity is important, but the design of the system matters too.
Rainwater Terrace combines rainwater storage with integrated planting, meaning your water butt can become part of your garden rather than something you feel you need to hide.
The system uses a through-flow design where rainwater moves through the containers, with excess water returning to the drain once the system is full. This continual flow helps keep the stored water fresher and avoids the stagnant-water problem associated with some conventional storage approaches.
The integrated planters are another difference.
They can be used for flowers, herbs, leafy salads and other plants, while capillary watering helps deliver water to the plants.
And because Rainwater Terrace is modular, you can build your system around the space you actually have.
So, which water butt size should you choose?
Here's the simple version.
🌱 Small patio or compact garden
A good starting point if you're mainly watering pots, containers and a few plants.
🌸 Average garden
Ideal if you have borders, containers, hanging baskets and regular watering requirements.
🍅 Vegetable garden or greenhouse
More storage gives you a useful reserve when your plants need regular watering.
🌿 Large garden
Consider larger storage or multiple connected systems if you're watering extensive planting.
💧 Not sure?
Start with a modular system.
One of the biggest advantages of Rainwater Terrace is that you don't have to decide how much storage you'll need for the next ten years.
You can start smaller and add more capacity when you need it. Water butt connector kits can be used to link systems together.
Don't forget the downpipe
Before ordering your water butt, check the type and size of your downpipe.
Your rainwater diverter needs to be compatible with your existing system.
Rainwater Terrace offers diverters and adapters for different UK downpipe configurations, making it easier to connect your water butt to your home's rainwater collection system.
If you're unsure which adapter you need, it's worth checking before ordering.
The best water butt is the one you'll actually use
Ultimately, choosing a water butt isn't just about buying the biggest capacity.
It's about finding a system that works with your garden, your roof, your watering habits and your available space.
For some people, that's a compact 67 litre system.
For others, 200 litres will be a better fit.
And if you're growing lots of plants, managing a greenhouse or simply want to make the most of every drop of rain that falls on your roof, 268 or 400 litres could be the better option.
The advantage of a modular system is that you can adapt as your needs change.
Ready to start collecting rainwater?
Rainwater Terrace makes it easy to collect, store and use rainwater in your garden – while adding attractive planting space at the same time.
From compact 67 litre systems to 400 litre modular rainwater harvesting systems, there's a configuration to suit different gardens, spaces and watering requirements.
Explore the Rainwater Terrace water butt range and find the right system for your garden.
Shop Rainwater Terrace Water Butts
Frequently Asked Questions
What is the best size water butt for a small garden?
A 67 or 134 litre water butt can be a good starting point for a small garden, patio or courtyard. The right size ultimately depends on how much planting you have and how frequently you water.
Is a 200 litre water butt big enough?
For many average-sized gardens, 200 litres provides a useful amount of rainwater storage. If you have extensive planting, a greenhouse or a vegetable garden, you may benefit from additional capacity.
Can you connect two water butts together?
Yes. Rainwater Terrace is designed as a modular system, allowing additional units to be connected to increase your total rainwater storage capacity.
Is a larger water butt always better?
Not necessarily. A larger water butt provides more storage, but you also need to consider the space available, your roof collection area and how much water your garden actually uses.
How much rainwater can a water butt collect?
The amount depends mainly on your roof area and rainfall. Even relatively small amounts of rainfall can produce hundreds of litres when collected across a sizeable roof.
What size water butt do I need for a vegetable garden?
For a vegetable garden, consider at least around 200 litres of storage, with larger capacities useful for extensive growing areas or greenhouses.
Can I increase my water butt capacity later?
Yes. This is one of the advantages of a modular rainwater harvesting system. Rainwater Terrace units can be connected to increase your storage capacity as your needs grow.
Where should I put my water butt?
Choose a stable, level location close to a suitable downpipe and ideally somewhere convenient for watering. Also consider how the water butt will fit into your garden and whether you'll be able to access the taps easily.
Make every drop count
You don't need a huge garden to benefit from collecting rainwater.
You don't need complicated plumbing.
And you don't need to predict exactly how much water you'll need for years to come.
Start with the space you have, choose a sensible capacity and build your rainwater storage around your garden.
Because when the rain comes, it's worth keeping it.