Should You Use Rainwater to Water Your Houseplants?

"Is Rainwater Better for Plants?"

Rainwater is perfect for plants. They've evolved over millions of years with rain falling onto their leaves and soaking into the growing medium surrounding their roots.

Many will argue that rainwater is often one of the best options for maintaining healthy plants. It's true that it's natural and free as well as having beneficial affects for most houseplants.

So to answer this question, yes, you can use rainwater with great results, and your plants will likely love you that extra bit more if you do. But you don't have to use it. As a houseplant lover who has been growing them for decades, I rarely use rainwater. There are reasons for this which I'll cover below.

A water butt holding rainwater that has come down an attached drainpipe

Why does rainwater make plants so much happier than tap water? Let's find out.

In this post I'm going to explore three broad topics, covering why rainwater is good for plants, and can make them happier than using tap water. Before looking at how to collect, store and use rainwater properly.

I'll add tons of top tips, dos and don'ts as we go, that should hopefully give you some ideas you can use in your own watering setup.

Contents of this Guide

Benefits of Using Rainwater for Houseplants
How to Collect Rainwater
Best Practices for Using Rainwater

Benefits of Using Rainwater for Houseplants

"Why does rainwater make plants so much happier than tap water?". This is the question I was asked that inspired this article. The exchange happened with a friend after a brief thunderstorm during a hot summer. The rain fell, then it stopped and the sun came out. It smelt glorious and I agreed the plants and greenery looked fantastic.

Part of this is simple physics, the water droplets reflecting the light and making everything look brighter and shinier, but there is some science that rainwater can give plants a little boost.

Rainwater droplets on the leaf of a Silver Sword Philodendron

There is something about outdoor plants looking happier after a rain shower. Replicate this by using rainwater to rinse dusty leaves for a refreshed appearance (cleaning the leaves can also improve photosynthesis. A double win!)

Natural.
Rainwater is naturally soft water, meaning it has a low mineral content compared to tap water that is often classed as hard water.

Hard water contains higher levels of calcium, magnesium, and other minerals. Although these minerals can benefit plants in small amounts, constant use of hard water can cause a buildup in the soil. This could then lead to salt buildup and increase the soil's PH levels into the alkaline range.

This is a gradual process and most plants can adapt, but it can reduce plant health and slow down the speed of growth. Rainwater will prevent this from happening.

Does using Rainwater replace the need to fertilize plants?
It's true that rain does contain nutrients. However, as this study and this research shows, the amount of nutrients overall is low. So you'll have to continue to provide fertilizer to your houseplants for the best results.

Contains Nutrients.
Plants need nitrogen in reasonable high amounts. It's used primarily for leaf growth, so if you have a fast growing plant, more nitrogen the better in some cases. The atmosphere contains nitrogen and when there is lightening this energy converts atmospheric nitrogen into nitrates which dissolve in rainwater before falling to earth. Collecting it can give you nutrient water for your plants.
No Chemicals.
Most countries treat their water supplies with chemicals like chlorine, chloramine and fluoride. This ensures clean healthy water comes out of our taps, but some plants are sensitive to these chemicals. Additionally, they can harm the beneficial microorganisms in the potting mix surrounding your plants roots. Damaging these delicate micro ecosystems can stress your plant or make its growth and health less vigorous than it would be from using rainwater.
Eco-Friendly and Free.
Rainwater is free, reducing your water bill. It also reduces reliance on using other sources of water like bottled or tap water, which can sometimes be scarce in some countries. It's also good for the environment to reduce storm water flowing into sewer systems.

Yellow watering can being filled with tap water from a running tap

It's generally fine if you water plants using tap water. But if you have hard water then overtime it can affect the potting soil and affect plant growth.

As well as the benefits outlined above, sensitive plants like Ferns (i.e. Boston, Maidenhair Fern etc) and Carnivorous plants (i.e. Venus Flytraps, Pitcher Plants etc) can be very fussy with hard tap water. So in this instances if these are houseplants you want to grow, you may well find you have to explore the idea of harvesting rainwater.

Hi, I'm Tom!

If you're like me and enjoy the challenge of growing houseplants and getting them to thrive, then Ourhouseplants can help. This website shares my knowledge and years of growing plants and provides (hopefully) helpful advice on properly caring for your indoor plant friends.

How to Collect and Store Rainwater

If you're sold on using rainwater on your plants you're going to need to know how to harvest and store it properly. The good news is that humans have been collecting rain for centuries and we're pretty good at it.

It might sound like a simple case of putting out a watering can or tray when rain is forecast to catch it. Although that does work, it's not practical. You'd only collect a trickle even in a heavy downpour. Hardly enough for even one plant let alone a small collection.

The amount you can gather will depend on the surface area that it's collected from. If you want large amounts of water, you're going to need to think bigger. For most people the straightforward way of doing it is to use a water butt or storage tank.

Outdoor rainwater storage tub with a lid to prevent debris and insects.

They're extremely popular in some countries. For example I'm from the UK and many developers build new homes that come with these rainwater storage barrels as standard. If you don't already have one, they're still easy to retrofit provided you have a downpipe and some space.

Too little space for a normal water barrel?
If you're happy to spend a little more for one, some companies now make unusually shaped Slimline Water Butts like these.

They should ideally come with a lid or cover. Standing water is a magnet for insects like mosquitoes, open tubs will inevitably also have debris and other organic material falling in. Over time this will encourage bacteria, making the water smelly and potentially harmful for your houseplants when you come to use it.

However you might share my problem, in that you either don't have access to downpipes or sufficient space to install the barrel. Although I have two pipes, both are in unsuitable locations.

Can I use something other than rainwater?
If rainwater isn't an option for you, you could try other options. Water from a dehumidifier, distilled water and boiling water that's been allowed to cool could all have benefits over tap water.

Fortunately there are now tubs in different sizes including super slim. They hold less water but are great for awkward positions. I've considered them, but they can be five or six times the price of a standard water barrel. When the price falls I'll be first in line to get one.

If you're in a flat, apartment, condo or have no access to property downpipes then you have to get more creative.

I've seen setups involving connections to garages or even garden sheds. Collecting snowfall and letting it melt is another popular method, but obviously it's extremely seasonal. You may know someone who has a barrel and they're happy for you to take the water. As long as it's clean and you store the rainwater correctly (more on this next) this could work too.

Best Practices for Using Rainwater

Although it's natural, rainwater does go bad, and there are types of rain you shouldn't use on your plants. Here are the dos and don'ts to be aware of.

Avoid stagnation.
Stagnant water can develop harmful bacteria, algae, or fungi, which can smell pretty bad. It may also harm your plants. To prevent this, use rainwater within a week or two of collection or if you're storing it in a sealed bottle or container, keep it in a cool, dark place to slow microbial growth.
Combine with Fertilizer.
Rainwater's natural softness allows nutrients from fertilizers to dissolve more readily, enhancing absorption by plant roots.

Are mushrooms more common when using rainwater?
If organic material is allowed to collect in a water storage container it can increase the chances of mushrooms and toadstools growing in a potting mix. But there are other reasons for mushrooms and it's not always a bad thing to see.

Filter if necessary.
Rainwater is generally safe but it may pick up impurities during collection, such as dust, pollen, or debris. Filtering the water through a fine mesh or using a filter to create filtered water can remove any unwanted particles and reduce weeds and mushrooms sprouting in the potting mix.
Use it as fresh as possible.
It's best to use it as soon as possible. Don't store it for weeks and weeks "just in case". It's better to use it while fresh and if you run out switch back to tap water until rain falls again.
Take care with roof runoff.
Most rainwater is collected from a roof, and this is usually fine. But prolonged periods of dry weather can mean contaminants accumulate over time such as chemicals from roofing materials, mold, or bird droppings. The rain arrives and all of this junk flushes down which you then feed your plants. So after a long dry spell it may be best to use the collected rainwater on your outdoor plants (or use some kind of filtration system, see above point).

Water tub with a white downpipe allowing water to flow into a open container. The container is filled with dirty looking rainwater

After a heavy rain shower this tub is almost completely filled. However if you're using water from a barrel that doesn't have a lid like this one, the water will need to be used quickly before it goes bad.

Don't use dirty water.
If it smells or looks dirty, then don't risk it on your plants. You're adding something that is rotting and will potentially upset the soil biome surrounding your plants roots.
Don't collect storm water from roads, parking lots or sidewalks.
These places might seem ideal spots to collect water from, but they accumulate significantly more dirt and chemicals then the common roof.

You can mix with tap water when needed.
Houseplants will adapt and grow almost as well if you use tap water. If rainwater is unavailable in sufficient quantities, mixing what you have with tap water can still reduce the overall mineral content.

Don't stress if you have a dry spell.
Rainwater collection is weather-dependent, meaning it may not always be available, especially during dry seasons. If you live in a country with only occasional rainfall, your storage will run dry eventually. Don't worry about it.
Don't use very cold water.
Avoid using cold rainwater straight from storage, especially over the winter months. Let it reach room temperature before watering to prevent shocking your plants.

If you use it correctly, rainwater can be better for plants than tap water. In reality for most people the difference you're likely to experience with your plants is limited, but every little helps.

If you live in a very hard water area or have problems using tap water with your houseplants, you may have to use alternative water sources to continue with this hobby. Rain water is free and will help in these situations, so do give it a go if you're able and see if you notice a difference.

About the Author

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Tom Knight

Over the last 20 years, Tom has successfully owned hundreds of houseplants and is always happy to share knowledge and lend his horticulture skills to those in need. He is the leading content writer for the Ourhouseplants Team.