Is RO Water Good or Bad for Plants?
Written by: Alexandra Uta // Last Updated: Aug 25, 2023
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Struggling to keep your plants alive and can’t figure out why? It could be your water.
Not all water is created equal, and some kinds are much better for your plants than others.
Does RO water fall into this category? Read on to find out.
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Key Takeaways
- Reverse osmosis water is good for plants, but it is essential to remineralize it, so the plants do not miss out on any nutrients they need for growth.
- The only times when RO water may be damaging to plants is if it is not remineralized and the plants consume ‘dead water’ for some time or if the pH is out of balance.
Is RO Water Good for Plants? Is It Safe?
The great news is that RO water is safe for plants and is considered one of the best kinds of water to use for irrigation.
Reverse osmosis filtration systems remove many dangerous contaminants that are harmful to plants and are recommended above other kinds of water for more delicate plant varietals.
When and Why to Use RO Water for Plants
RO water can be used for any plant, as it allows more control over exactly what your plants are being exposed to.
With the removal of contaminants from RO water, what goes into your soil is pure water with no nasties that may harm the plant. This allows you to control what nutrients the plants get as long as you use the appropriate fertilizers.
When Reverse Osmosis Water Is Bad for Plants
Reverse osmosis water can be bad for plants if you do one or both of these things;
- Give the plants the RO wastewater,
- Or do not use any fertilizers or solutions to give your plants the good minerals that an RO filter removes.
What Is RO Water?
Reverse osmosis water has been filtered through a membrane that traps impurities on one side, allowing the clean water to flow to the other side without them.
A reverse osmosis system is capable of removing common contaminants from water, such as iron, manganese, chlorine, heavy metals, bacteria and viruses, pesticides, and herbicides.
Further Reading:
Benefits of Using RO Water for Plants
RO water is good for your plants. Your water supply will always be consistent, allowing you total control of what nutrients your plants will get once you add fertilizer.
Contaminant Removal
As mentioned before, RO water purification can remove a whopping 99% of contaminants, such as lead, arsenic, and other toxic chemicals that are harmful to your health and the health of the plant. This means the plant will grow without those harmful chemicals as part of its makeup, which is particularly great if you are growing plants you plan to eat.
It will also remove dissolved salts, such as potassium, phosphorus, nitrogen, magnesium, and calcium. This could be detrimental, so it is important to remineralize the soil with the appropriate solution or fertilizer.
Chlorine
The carbon pre-filter actually removes chlorine in a reverse osmosis water filter system. Too much chlorine in plant soil can lead to the death of the plant roots, although usually, the amount found in municipal tap water is not considered high enough to be of any concern unless in particularly chlorine sensitive plants.
You Know Your Water Quality
One of the main reasons why many botanists recommend RO water is because you know exactly what kind of water is going into your plants. It’s like a neutral base of pure hydration that you can add to with the minerals your plant needs. It takes the guesswork out of wondering if your plants have too much of something and not enough of something else.
Boost Plant Growth
Certain minerals, such as sodium, can affect plant growth and even kill your plants if there is too much of it in the water. As RO removes most dissolved solids from water, this is no longer a concern, and your plant growth may improve.
Drawbacks of Using RO Water for Plants
RO water can be bad for your plants, mainly if you use only RO water without any remineralization.
Beneficial Minerals Are Removed
As mentioned earlier, RO water removes almost all the minerals in the water, both the bad and the good! Your plants do need certain minerals in the soil in order to thrive, and taking away their mineralized water source would be detrimental unless you use some kind of solution or fertilizer to remineralize the soil.
Acidic Water
Reverse osmosis water can be slightly more acidic than other kinds of water. Usually, this isn’t too much of an issue as the soil will buffer it, but it can possibly make it harder for the plants to absorb nutrients due to changes in the soil pH.
Cost
Compared to regular tap water, reverse osmosis water does cost a lot more, both in the initial upfront investment, plus maintenance of the RO system and increased water usage.
Some may consider it a small price to pay for pure water for a household’s inhabitants, plants, people, and animals, but it is something to consider before purchasing.
System Maintenance
A reverse osmosis system must be regularly maintained, having the filters changed over on schedule, or it won’t work. This is usually simple enough to do on your own but requires an extra task added to your to-do list often, plus some additional costs.
What to Add to Reverse Osmosis Water to Help Your Plants Grow?
With the exception of increased costs and extra maintenance, the aforementioned disadvantages have a solution: to add the minerals back in with fertilizer salts! For this, we need to look at two things, optimum total dissolved solids (TDS) and pH levels of the plant water.
Optimum TDS and pH Levels of Plant Water
Different plants will require different levels of TDS to stay healthy. For example, most hydroponics need a TDS level of around 800. Other plants like bok choy need about 1500. If the TDS in the plant soil is lacking, it will affect the ability of the plant to grow.
Also, most RO water has a pH of between 6.0 and 6.5, which is optimal for plant growth. However, should your RO water fall outside these pH levels, it can lead to various issues in your plants, such as stunted growth, necrosis, leaf death, and brown spots.
The Solution: Remineralization
RO water eliminates dissolved salts, so it is important to use fertilizer salts to put them back in. Some fertilizers have a higher SI (salt index) and different nitrogen, phosphorous, and potassium levels.
Factors such as what plant you are growing and its growth stage will determine what SI you need and what level of TDS you should aim for.
It is also important to test your water regularly to ensure the pH is within range.
RO, Filtered, Distilled, Softened, Tap, Well, Rain, Spring – Which Water Is the Best for Your Plants?
While remineralized RO water is considered great for your plants, what about the other kinds of water? Is RO the best, or are there better alternatives?
Distilled Water
Similar to RO water, distilled water is better than tap water as it doesn’t have contaminants but needs to be remineralized.
Rain Water
Better than tap water, rain water doesn’t contain the fluoride and other chemicals and metals found in tap water. But it lacks minerals. Add them back in and your rain water will be ideal for your plants.
Filtered Water
Filtered water is acceptable for plants, but buying bottled or filtered water all the time can be pretty costly and not a particularly practical solution. Also, depending on the filtration method, it may only be mildly better than tap water.
Spring Water
Another great option for plants, this oxygen-rich water is just as good as rainwater and doesn’t contain any harmful chemicals either. Unless you have a natural spring nearby, though, it may not be practical.
Tap Water
Tap water is okay for most plants, but not very sensitive ones that the contaminants in the water could damage.
Aquarium Water
This outside-the-box option is a great one. Aquarium water is usually conditioned and pre-filtered, so it’s free of most contaminants. Then, the secret ingredient of animal waste from the fish acts like a natural fertilizer!
Softened Water
If you have hard water that has been softened, do not use it on your plants. Naturally soft water is fine, but the salts used to change hard water to soft water are not suitable for your plant growth.
Well Water
Well water can be okay for watering your plants, providing it is clean, bacteria-free, and has a suitable pH.
If you have any thoughts about the question, is reverse osmosis water good for plants, please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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