Is Hard Water Bad for Plants? [ANSWERED + SOLUTIONS]

Hard water, soft water, tap water and distilled water. All water is the same, right? WRONG!

Even though it is hard to visually tell the different types of water apart, the composition of water can differ greatly:

  • hard water has higher mineral content than others,
  • hard water can leave residue on plants’ leaves as it evaporates, and
  • hard water can change a soil’s composition that can affect a plants’ health.

In this article, at the Garden Bench Top, we will be discussing the impact of using hard water on your plants. You will understand how hard water interacts with your plants and soil. We’ll also highlight what indicators to look out for in your potting soil mix, as well as some alternatives to hard tap water that can be used to supplement your watering.

So if you’re ready, grab a coffee and get ready to answer the question is hard water bad for my plants?

What is Hard Water?

For the benefit of those that haven’t experienced hard water, we thought it would be useful to define what hard water is.

Hard water is water that contains a high amount of mineral content that it has absorbed from passing through substrates and deposits as it makes its way to the surface. Some minerals that it can contain include sulfates, magnesium, calcium, bicarbonates and many more.

mineral build up on home tap

Hard water exists in certain regions around the world, and is supplied to households as tap water. Note that, the mineral concentration in the hard water will vary around the world.

For this reason, in some countries using hard water for your plants will be perfectly suitable, whereas in other countries it can have a significant impact on your plants’ health.

Let’s look at how hard water can impact your houseplants.

Is Hard Water Bad for House Plants: Reasons to STOP

The problem with hard water is the high mineral content. Using hard water once may not have any detrimental impact on your indoor plants. However, over time, continued use has a cumulative effect.

Water Stains on Your Plants

One of the more noticeable effects you will see hard water has on your plants are the watermarks that remain on your plants.

If you haven’t seen it before, it looks like someone has mixed chalk with water and splattered it all over your plants’ leaves.

hard water stains on leaves

This occurs when water falls onto the leaves and evaporates, leaving the minerals behind and staining your gorgeous leaves.

Not only is this unsightly, the residue actually hinders your plants’ ability to photosynthesize, which is a process that is necessary for your plant to generate glucose to grow.

Hard water stains prevent your plant from being able to photosynthesize and produce food for itself.

Recommended Reading:

If you have hard water stains on your leaves, we recommend cleaning them off to make your plants look great and allow them to photosynthesize. Check out our article for our plant-friendly DIY recipes for cleaning solutions.

Makes your Plants Dull

Another impact hard water stains can affect your plants, is making them lose their color and become dull.

The mineral build up on the plants’ leaves limits the amount of light that a plant can absorb. Without adequate sunlight, the plants’ chloroplast cells (pigment cells) cannot be stimulated to produce chlorophyll – which is the vibrant green color you see on healthy indoor plants.

Consequently, making your plant appear dull and colorless.

Calcium Carbonate Deposits on the Potting Soil

Hard water with a significantly high mineral content can even begin to change the water absorption levels of the soil in your containers.

As hard water is continually poured into your soil, some minerals can remain and accumulate. It can even become visible on the surface of the soil with off-white clumps of mineral deposits. Check out the image below where one of our community experienced salt and calcium carbonate deposits in her indoor plant soil.

build up of calcium deposits

If the mineral deposits are not removed, they can form a mineral layer that can eventually resist water, which reduces the available water in for your plant.

Avoid Using Water with Chlorine

Water that includes a percentage of chlorine is not compatible with plant life. Chlorine is added to tap water to sterilize it and eliminate any unwanted living organisms such as bacteria.

And it is for this reason why it should not be used to water your plants. Your plant is a living organism, and chlorine will kill it.

Chlorine is toxic to plants.

What to Use Instead of Hard Water (SOLUTION)

So now we know why hard water shouldn’t be used for plants. What water is okay to use for watering your plants?

Water Check – How Hard is Your Water?

If you live in an area that has hard water supplied to your home, we recommend checking the composition of your water (or how hard it is). Like we said earlier, some hard water is okay to use with plants.

You can call your local municipal water authority and inquire about the hardness level of your local water.

The US Geological Survey, uses the following scale to measure water hardness.

ClassificationMg/LGrains per Gallon (gpg)
Soft0 – 17.10 – 1
Slightly Hard17.1 – 601 – 3.5
Moderately Hard61 – 1203.5 – 7.0
Hard121 – 1807.0 – 10.5
Very Hard180+10.5+

You can use a water test kit to determine the MG/L value of your water and compare it to the table above. Basically, if your result is greater than one grain per gallon (17.1 mg/L or less), your water is hard.

Use Filtered Water or Distilled Water

Even though our tap water is not considered hard water, we still prefer to use distilled or filtered water for our plants.

Filtered water (like bottled water) is as it sounds. It is water that has all the unnecessary water minerals and chemicals filtered out, so all you have is the good stuff leftover. To filter out the unwanted elements, water is put through a filtering process that involves running it through materials that remove toxins (like carbon).

On the other hand, distilled water is produced by running the water through a boiling chamber until it evaporates. The evaporated water is then cooled and condensed into pure H2O, ready to be used to water your plants.

Collect Rain Water

An alternate source of water that you can use for your plants is rain water. Rain water is nature’s own water source, so if it is good enough for mother nature, it should be good enough for your indoor plants.

When collecting rain water, make sure the water hasn’t been stagnant for too long. Stagnant water can become contaminated with algae, which will stunt the growth of your plants.

What’s Next?

Using hard water to hydrate your plants is not the end of the world. It can be used in the short term if you are in a bind without any other options.

However, we would recommend looking for alternate sources like filtered, distilled or rain water for a longer term solution.

Longer term use of hard water for plants will be problematic and likely end in frustration and disappointment.