Water is not “just” water. Even though it seems to be a transparent, tasteless liquid, it comes with a wide variety of dissolved nutrients which can have different effects. For an appropriate diet for your indoor plants, it is essential for you to know what type of water is best for your plants.
Generally, rainwater is best for houseplants due to its high nutrient and oxygen levels. It is best harvested avoiding any external interferences that cause contaminations. Recommendable alternatives are fish tank freshwater, filtered tap water, or distilled water in combination with fertilizer.
In this post, I will share in-depth knowledge about plant water with you as well as give you great tips to know what water is best for your plants and how you can provide that good quality water without much effort.
What Defines Water Quality and How It Affects Plants
What Defines Good Water Quality for Plants?
Before we get into any details about the different types of water and why they are good or bad for plants, we need to know what characteristics are actually important for plant water. What factors define good and healthy water quality for plants are the following:
Healthy, good quality plant water contains essential nutrients, an adequate oxygen content as well as the least amount of toxins possible.
What Are The Essential Nutrients for Plants?
As the Department of Primary Industries of New South Wales states, there are three main nutrients any plant needs:
- Nitrogen (N): Key element in plant growth
- Phosphorus (P): Promotes transfer of energy from sunlight to plants, stimulates early root and plant growth, and speeds up maturation
- Potassium (K): Promotes transport of nutrients in plants, boosts metabolism, and increases vigor and disease resistance
These three major elements are also often referred to as NPK and form the basis of plant food. In addition, plants need a certain amount of:
- Calcium (Ca): Key element in root health, growth as well as the development of leaves
- Magnesium (Mg): Key component of chlorophyll and hence vital for photosynthesis
- Sulfur (S): Involved in energy processes of the plant such as producing odors and flavors
Furthermore, plants need certain trace elements such as iron, manganese, zinc, copper, boron, and molybdenum. They are called trace elements as the plant only needs very small amounts – traces – of it regularly.
What Happens If You Use Bad Quality Water for Your Plants?
If you water plants with bad quality water, you might not notice bad effects on your plants in the short run.
Over time though, there are several long-term consequences to watering with bad-quality water:
- The build-up of substances on the top layer of the soil: As excess substances accumulate in the top layer of the soil, visible as a white crust, the capacity of the soil to absorb water is reduced.
- Weak immune system: Accumulation of too many of the wrong substances, such as fluoride or chlorine, within the soil, weakens the overall immune system and health of the plant.
- Prone to pests and diseases: The weaker a plant gets, the more prone it is to any kind of pests or diseases (just as humans are more prone to get sick when their immune defense is low).
- Dying plants: Finally, if no improvement is made in regard to the water being used, the plant might die off.
In short: Watering with bad-quality water will in the long run lead to nutrition deficiencies in your houseplants. What a lack of the main nutrients causes within a plant is very well explained in this short Youtube video:
The Best Water for Houseplants is Rainwater
The best water for houseplants is that which is healthiest for them. Given the above definition of good quality water, we are looking for the type of water which contains the most nutrients, oxygen, and the least contaminants. Rainwater fulfills all of these prerequisites and is the healthiest plant water you can find.
Rainwater has been studied for its chemical components since the beginning of the 19th century and it has long been shown that it plays an important role in the nutrient cycle of ecosystems, as Allen et al. state in their article in the Journal of Ecology (1968).
“In the past 15 years […] it has been clearly shown that rainfall nutrients play an important part in the nutrient cycle of ecosystems”
(Allen et al. 1968:497)
In regard to plant nutrients, rainwater carries all essential nutrients that make plants happy: Nitrogen, phosphorus, potassium, calcium, magnesium, sodium as well as occasionally sulfur.
Complete Overview and Ranking: Types of Water and Characteristics
First of all, it is important to know what types of water there are that you could use to water your plants. Most people would mainly be thinking of tap water or if you are already into plants, rainwater or distilled water might pop up when thinking about the matter.
There are many more options though – and many of these types of water can be prepared in specific ways to suit your plants better.
I will give you plenty of helpful tips on how to prepare the best water in a minute, but first I want to share with you a complete overview including a ranking of all possible types of water as well what their benefits and downsides are.
| Health Ranking | Type of Water | Pro’s | Con’s |
|---|---|---|---|
| 1 | Rainwater | + High nutrient levels + High oxygen level + Low levels of toxins or contaminants + Slightly acidic | – Low Disposability: Water changes in fish tanks don’t give enough plant water on a regular basis – Need to maintain a fish tank – Applies to only freshwater fish tanks |
| 2 | Fish Tank Water (Freshwater) | + High nutrient levels + High oxygen level + Natural fertilizer from fish excrement + No toxins or contaminants | – Low Disposability: Water changes in fish tanks don’t give enough plant water on regular basis – Need to maintain a fish tank – Applies to only freshwater fish tanks |
| 3 | Filtered Tap Water | + Good nutrient levels + Very few toxins or contaminants | – Efforts or costs to filter water – Lower oxygen level |
| 4 | Distilled Water | + No toxins or contaminants + Pure Water | – No nutrients at all – Low oxygen level – Not eco-friendly if bought in plastic containers – Costs |
| 5 | Reverse Osmosis (RO) Water | + No toxins or contaminants + Pure Water + Integrated in your household tab system | + No toxins or contaminants + Pure Water + Integrated into your household tab system |
| 6 | Bottled Spring Water | + High nutrient levels + Very low levels of contaminants | – Not eco-friendly – Produces a lot of plastic waste – High costs |
| 7 | Water from Pond, Stream, Lake | + High nutrient levels + Natural fertilizer ingredients | + Readily disposable + No additional efforts + Good quality tab water contains good levels of nutrients |
| 8 | Unfiltered Tap Water | – Depends on the living area – Can contain harmful ingredients such as fluoride, chlorine or bacteria – Soft tab water contains too much sodium (salt) for plants | – Depends on the living area – Can contain harmful ingredients such as fluoride, chlorine, or bacteria – Soft tab water contains too much sodium (salt) for plants |
1. Rainwater – The Nutritious Winner
Rainwater is the clear winner for plant water due to its high nutrient and oxygen levels. It contains nitrogen, phosphorus, potassium, calcium, magnesium, sodium as well as occasionally sulfur, and is well endowed with oxygen. Furthermore, it is slightly acidic water and contains no treated chemicals as tap water does. All your plants need is right there!
That rainwater wins the prize for best plant water obviously makes sense as this is the water that naturally waters plants on this planet. But there can be manmade downsides to it: If you live in an area with high population density or near an industrial area, the rainwater won’t be ideal as it takes up some of the contaminants present in the air.
2. Fish Tank Water – Fertilized By Fish
This is a type of water that is often neglected in plant care. Freshwater fish tanks have amazing water that you can use for your plants. It is full of nutrients given off by organic matter such as from algae. Fish excrement even makes it a great fertilizer!
It is not the most disposable source of water though, as first of all you need to own a fish tank or know someone who does and the leftover water from water exchanges in the tank is usually not enough to regularly water your plants.
That said, if you can get your hands on some fish tank water every now and then, it will be a great addition to your watering routine.
Note: As you can imagine, this only works with freshwater fish tanks!
3. Filtered Tap Water – Great Disposability
Tap water is a great water source as it is readily available in any household and comes at no extra cost. Though in many regions, treated chemicals are added to it such as fluoride and chlorine.
If you filter your tap water, you will get very good-quality plant water.
There are many quite simple ways to filter your tap water, it doesn’t take that much effort to turn your regular tap water into filtered water ready for your plants.
4. Distilled Water – The Purest But Least Nourishing
Distilled water is the cleanest and purest water of all types. It is made by boiling water into vapor and then collecting the condensed vapor in a separate container. Through this process, all contaminants or ingredients are distilled out of it and there is nothing in it that could harm your plants.
This doesn’t make it the healthiest plant water though: In the distillation process, all nutrients are also eliminated. That is why you should only use distilled water on your plants in combination with fertilizer.
5. Reverse Osmosis (RO) Water – The Fancy Option
Another less-known type of water is called reverse osmosis water (RO Water). The aim here is similar to distilled water: Instead of distilling out unwanted ingredients, water goes through several filtration processes until all unwanted ingredients are eliminated. In the last step, healthy minerals are added back to the water.
This sounds very good but requires installing an expensive filtration system in your household. This is why I consider it to be not the favored option as most people won’t be able to install such a system due to its high initial costs.
6. Bottled Spring Water – Packed in Plastic
What about bottled water? Bottled natural or spring water is healthy water due to its nutrient and oxygen levels and there will be no toxins or contaminants in it.
I would not recommend regularly using bottled spring water for your plants, as it produces a lot of plastic waste with all the packaging. It is probably the least eco-friendly way to water your plants and there are other options that are just as beneficial for your plants.
Note: Do not use sparkling water or any type of soda for your plants. Sparkling water is very acidic and while some acidic plants might like it, others will not. Soda contains a lot of sugar which is harmful to your plants.
7. Water from Ponds, Streams, and Lakes – Dependent on Environment and Data
Ponds, streams, and lakes are water bodies that can be valuable sources of good-quality water with a lot of healthy nutrients and oxygen, similar to rainwater or fish tank water.
The problem with water bodies is that the quality of water varies a lot according to season and location. While the quality might be good in winter, it can drastically change in summer.
If you want to use water from a pond, stream, or lake, make sure to always check the local official data on its water quality for your location (if it exists) or let the water be tested every couple of weeks. In the long run, this might be a bit too much effort when other water sources such as rain or filtered tap water are much easier to access.
8. Unfiltered Tap Water – Good Quality Only
Last but not least, unfiltered tap water can be a very good option to water your plants. Having it as the last option here might seem a bit contradictory to that statement. The thing is just that it depends a lot on where you are living and what quality your tap water has.
If you live in a place with high-quality tap water with almost no chlorine, fluoride, or other harmful chemicals and bacteria in it, your plants will have no problems with regular tap water. Myself, I live in a place with amazing tap water and use it regularly to water my plants without further doubts.
Though if you live in an area with highly chemically treated tap water or even in a place where it is not safe to drink tap water, then I highly recommend not using unfiltered tap water for your plants.
This is why unfiltered tap water comes last in this ranking and is limited to good quality tap water.
How to Know If Your Tap Water Is Good Enough for Houseplants?
The specifications you mainly need to know about your tap water are the following:
Hard or Soft Water: Water Hardness Levels of 30 – 60 ppm are ideal for plants
Water hardness levels are measured by milligrams of calcium carbonate per liter and reported in the unit parts-per-million (ppm).
Water hardness levels of 30 – 60 ppm are considered ideal for plants.
Water harder than that will contain too many calcium and magnesium ions (too many limescale deposits), and water softer than that will contain too many sodium ions (too much salt).
If you are cleaning off limescale deposits in your kitchen and bathroom regularly, then your water is probably too hard. To find out exactly what hardness levels your tap water has, you can check out the regional authorities’ official data on tap water or you can get it tested in a laboratory.
pH Level of Water: Plants Prefer Slightly Acidic Water of 5.0 to 7.0 pH
As a general rule, plants prefer slightly acidic soil. To achieve this, plant water used needs to be slightly acidic as well.
The pH scale defines whether water is acidic or alkaline. On the pH scale, a level of 7.0 is considered neutral or balanced between acidic and alkaline.
A pH level between 5.0 and 7.0 is considered ideal for plant water.
Tap water generally has a pH level of anywhere between 6.5 and 8.5. Check with your local authorities’ official data on tap water what the pH level is or get your water tested in a lab.
Levels of Chlorine and Fluoride: 50 ppm of Chlorine and 1 ppm of Fluoride at the Max
As to the tolerable levels of chlorine in plant water, there are different opinions among plant experts. Some state that the upper limit of 5 ppm of chlorine per liter, as required by the WHO, is the maximum that plant water should contain. Other sources speak of limits as high as 100 ppm of chlorine for plant water.
Chlorine is not per se harmful to plants. If only low quantities are present in plant water, the plants will barely take it in. High amounts though can damage foliage growth.
Hence I recommend using water with 50 ppm of chlorine at the max.
Fluoride instead can be very harmful to plants. Plant water should contain no more than 1 ppm of fluoride per liter. Less is always better.
To find out how much chlorine your tap water contains, take a smell: If there is that strong chlorine smell to it, there is certainly too much of it. Here as well, you can check the local official data of your tap water or get it tested. As you cannot smell the fluoride levels, the only way to know about it is the official data or to test it.
7 Tips For Providing The Best Water For Your Plants
The above ranking is made with regard to the healthiness of your plants. Though in real life, you need to consider what type of water you easily have access to on a regular basis. Watering plants is a routine business and shouldn’t take great effort or cost each time to get the right water for your plants.
Rainwater might be the healthiest water out of all, but it is not within everyone’s reach on a regular basis. Maybe you have no option to collect it or you are living in a dry region with only little rain.
This is exactly why I think it is important not only to know what water is best for plants in general, but how you can prepare the best water for your plants given your specific circumstances. I will give you some helpful and easy tips on how to go about preparing good-quality water for your plants.
Don’t fret if collecting rainwater is out of your league – implementing any of these tips gives better water than just using regular tap water!
1. Collect Rainwater (Best Option)
There are several ways you can collect rainwater yourself:
- Set up rain barrels at your house: If you live in a house, you can set up rain barrels that are attached to the gutter system of your roof. They will collect and store so much rainwater that you can water your garden and houseplants with it.
- Place jars or open containers outside: Not everyone has a big garden or a house, but you can do with less to collect enough water for your indoor plants. Just place some jars or containers anywhere outside where it will rain on them. This can be a balcony, wide window shelves, terrace, beside the entrance door to your building. As long as it is a place where they can fill with rain, it’ll work.
- Place your houseplants outside when raining: This is a summer-only method unless you live in a year-round mild climate. Water your plants directly with rainwater by placing them in an outside area where it rains on them.
- Collect rainwater on a walk through your neighborhood: Next time it rains and you are at home, take some bottles and go for a walk. See whether you find any spots in your neighborhood where rainwater naturally collects, such as pots or empty bins standing around. Make sure it is clean before you fill your bottles with it. This method takes some more effort and you never know how much clean rainwater you’ll find, but depending on where you live it might be worth a try.
2. If You Can’t Collect It, Make It – How to Make Rain-ish Water At Home
As I have already mentioned earlier in this post, the water in a freshwater fish tank is great for plants. Not everyone has a fish tank, though. It is a lot of effort and takes some passion to maintain a fish tank at home. When I grew up, my dad used to have fish tanks and I remember how every weekend the living room was filled with different bins and pots for the weekly water exchange.
Even if you have no access to rainwater or to a fish tank, you can still use nature’s wonders to improve the water quality of your plants.
There are several water plant species that are known to clean toxins out of the water, purifying it and enrichening its level of dissolved oxygen. Doesn’t it sound great to have plants improve your tap water for other plants? Time to make your own plant water aquarium!
In ponds, the most common purifying plants used are among others the water hyacinth (Eichhornia crassipes), water iris (Iris laevigata), or the completely submerged hornwort (Ceratophyllum demersum).
Now, you probably don’t have a pond. As a type of water plant to add to a bucket of water, I would recommend using watercress. It propagates itself and grows very fast and makes for a great water purifier for your plant water bucket. Nice extra: watercress is edible, too. You can spice up your favorite salads with it!
Another option is duckweed which is also known to purify water. In ponds, it can become a nuisance as it is quite invasive and soon covers the whole surface. So be prepared to remove some every now and then.
If this option appeals to you: Set up a container, fill it with some sand and rocks, add your regular tap water, and add watercress or duckweed to it and let the plants do their work.
3. Use Filtered Tap Water (to Reduce Harmful Contaminants)
One of the easiest ways to get better water quality for your houseplants is by filtering your tap water. There are several ways to do that:
- Use a filter pitcher: In my opinion the easiest option. Buy yourself a filter pitcher (such as from BRITA).
- Add a faucet attachment in your kitchen: You can install a filter faucet in your kitchen. This works great but involves some costs.
4. Boost Your Plant Water By Adding Beneficial Natural Ingredients
There are plenty of natural ways to improve plant water, such as banana peel water, coffee, cooking water, eggshells, ashes, hair, and many more.
Not all ingredients have the same benefits and there can be bad side effects as well, so make sure you read all about what ingredients you can use when and how, as well as which are the most beneficial and effective in my post covering that whole topic.
5. Always Use Plant Water at Room Temperature
This is a general tip for improving your plant water routine: Whatever type of water you use, it should always be at room temperature. Water that is too cold or too hot gives the plant a shock and will damage its roots.
6. Make Unfiltered Tap Water Better By Letting It Sit for 1-5 Days
Even if you are not using any type of filter system for your tap water, there are ways to improve its quality for your plants:
- Let tap water sit for 1-5 days: With this method, most of the chlorine will dissipate and heavy metals sink to the bottom of the watering can. Make sure to not stir it too much before watering and only use the upper 2/3 of the can and pour the rest down the sink.
- Use meltwater: This is another method I read about, though I have never tried it out. Freeze tap water, then let it melt in a container. There should be sediments visible at the bottom. Only use the top layer or filter the sediments out before watering with it.
Another method you can read about on several websites is boiling your water to eliminate some toxins. Though that is true, boiling the water also decreases the oxygen level in the water, hence I would not recommend boiling it.
7. Make Your Own Distilled Water to Avoid Buying Plastic Containers
Distilled water is pure and contains no harmful elements. It is harmful for the planet though if you buy it regularly in plastic containers. A lot of waste can be avoided.
Now if you still want to stick to distilled water and have a hobbyist spirit: Why not set up your own water distillery at home?
I’ve found this Youtube video in which 9 DIY ways to set up your own water distillation system are explained wonderfully:
Frequently Asked Questions
How To Avoid Build-Up of Substances on Top of the Soil?
Having too much of a certain ingredient in the water can cause a build-up of substances on the top layer of the soil, such as a white crust that stems from magnesium or sodium excess. This layer can inhibit good water absorption in the soil.
But there are tricks to get rid of it:
- Renew the layer with fresh earth every couple of weeks or at least mix the earth a bit (without damaging the plant roots obviously)
- Use less fertilizer: As the crust can also stem from using too much fertilizer, try using less until the crust disappears.
What Indoor Plants Are Very Sensitive to Tap Water?
Not all plants react as sensitively to changes in water quality – just like we humans react differently to outside influences as well. In general, monocots are known to be more sensitive to regular unfiltered tap water than other plants. The following are the most common in households:
- Spider plant (Chlorophytum comosum)
- Red-veined prayer plant (Maranta leuconeura)
- Zebra plant (Calathea zebrina)
- Good luck plant (Cordyline terminalis)
- Peace lily (Spathiphyllum)
- All Yucca plants (Asparagaceae)
How to Know If My Houseplants Are Healthy?
Do you want to know how to check on your plants’ health? I recommend doing a quick health check regularly.
A plant health check includes:
- Checking the foliage: Color and appearance? Brown spots or edges? Burnt spots?
- Checking the stems: Color and appearance? Upright or wilting?
- Checking the root system: Overgrowth? Moldy smell?
- Checking the soil conditions: Absorbing water well? Too dry? Damp and moldy smell?
You can easily integrate checking their health into your weekly watering routine – that way you won’t forget about it.
Read all about these steps and what first aid measures there are for plants in need in this post: Step-by-Step Houseplants Health Check with First Aid Tips
How to Make My Houseplants Grow Better?
If you want to give your plants a nutrient boost and increase their resistance to pests and diseases, there are plenty of natural ingredients you can add to your plant water.
Lots of people recommend different ingredients, but how effective they are is not always sure. In my post on that topic, I give you a complete overview of all ingredients that are mentioned on the web and recommend those ingredients that I find to be the most effective and healthy ones for all types of plants.
Instead of changing up your watering habits, why not change life for your plants by playing them some music every now and then? Many studies show that certain sound vibrations stimulate plant growth. For more about what music plants like and other helpful tips, check out my post: Beethoven or Rap? What Effects Music Has on Your Plants’ Growth