The Best Water For Houseplants Explained

Water is essential for your plants to grow and flourish. The quality of the water you use can significantly affect the health of your plants as they are vulnerable to soluble salt buildup, chemicals, and hard metals. But what are the best options to water your houseplants with?

Rainwater is the best water for houseplants as it is oxygenated, soft, and rich in beneficial minerals. While tap water can be used depending on local water quality, distilled water is a better choice as it is void of contaminants or other chemicals. 

Keep reading if you are still at a loss about the best type of water to feed your plants. I’ll explain what makes good water quality, discuss the characteristics of the main water options, and share some additional things to consider.

Key Takeaways

  • Best Water for Houseplants: Rainwater is ideal due to its oxygenation, softness, and mineral content. Distilled water, free of contaminants and chemicals, is also a great choice.
  • Avoiding Tap Water Issues: While tap water can be used, its quality varies and may contain harmful chemicals and hard metals. To mitigate this, use distilled water or rainwater when possible.
  • Adjusting Water Quality: For tap water, letting it sit overnight can help evaporate chlorine. Boiling or filtering can reduce harmful minerals and contaminants.
  • Importance of Water Quality Factors: Pay attention to factors like water hardness, oxygen level, sodium content, boron concentration, water temperature, chlorine/chloramine levels, fluoride level, pH level, heavy metals, and salinity levels, as these significantly impact plant health.

What Makes Good Quality Water for Houseplants

Good quality water for houseplants means it is best suited to make a potted indoor plant flourish. Before drinking water, especially if it isn’t bottled water, you probably check to confirm it is clean and safe. Your plants deserve the same scrutiny because water quality matters to plants too. 

When looking at the water quality for plants, the following factors matter:

  • Water hardness
  • Oxygen level
  • Sodium content
  • Boron concentration
  • Water temperature
  • Chlorine/chloramine levels
  • Fluoride level
  • pH level
  • Heavy metals 
  • Salinity levels 

The presence, absence, and concentration of these components determine if the water is good or bad for your houseplants.

Water Hardness

The quality of water varies from country to country. In the US, hard water has over 61 mg of calcium carbonate per liter. In Germany and France, the concentration of minerals in hard water is 10 mg/liter.

On paper, these mineral details are based on water safety for human consumption—not so much for plants. The minerals in hard water bind the nutrients in the soil, making it inaccessible to houseplants. 

The challenge with hard water is the minerals increase soil salinity, evidenced by white deposits on the soil. The water also alters soil pH, making it more alkaline. When the soil pH is too high, it is harder for plants to access nutrients.

Oxygen Level

Oxygen level is an important indicator of good water quality. Dissolved oxygen is largely responsible for a healthy root mass. The healthy root mass boosts healthy plant growth, breaks down organic matter in the soil, and prevents root rot. 

Water with high levels of dissolved oxygen is naturally better for plants because it complements the oxygen in the soil. Rainwater and distilled water have the highest dissolved oxygen concentration, while tap water (hard water) has the lowest levels. 

Sodium Content

The total dissolved salts (TDS) in water determine the sodium content and water salinity. When hydrated, sodium has similar properties as potassium. If the soil is low in potassium, the sodium will boost root growth, enhance sugar and starch movement, and reduce energy loss. 

In higher concentrations, sodium is toxic to plants. Sodium finds its way into the soil in two ways: through hard water and when you use water softeners. 

Boron Concentration

Boron leaches from rocks, soil, and wastewater. It is also found in some fertilizers and pesticides.

In low levels, boron aids with cell and membrane formation in plants. It also aids with the movement of starch and sugar. 

Boron toxicity is worse in water containing chlorine and sodium. The effects include yellowing left tips and veins and dropping foliage. 

Water Temperature

Most of us naturally water plants without thinking about the temperature. However, water temperature is much more than hot or cold, at least when it comes to plants. It indicates dissolved oxygen levels and how quickly the plants absorb the nutrients. 

Water has higher oxygen levels at room temperature. Plant roots are more responsive to water with higher dissolved oxygen levels.

If the water is too hot or too cold, it can cause severe physical and cellular damage to plants. When watering plants, aim for a water temperature between 62 and 72 °F (17 and 22 °C).

Chlorine/Chloramine Levels

The chlorine or chloramine concentration in tap water is one of the reasons why it is bad for your plants. However, what’s worse is the chemical concentrations vary depending on how toxic the water is and the interventions implemented to make it safer. 

Although both substances work to disinfect tap water, it’s worth noting that they last differently in the water. It is also common for water treatment facilities to switch between these two substances, depending on the necessity.

Chlorine is a more effective disinfectant because it readily reacts with germs. As a result, the chlorine content may be used up by the time the water reaches house pipes. On the other hand, chloramine lasts longer in the water and cannot be removed simply through evaporation or by letting tap water sit overnight.

One day, you may water your plants with relatively safer water. On some days, the water may be more toxic

At low enough concentrations, organic matter in the soil can break down chloramines to safe and even useful levels. So, even if your plants initially appear unaffected by tap water, when chlorine or chloramine levels are higher, your plants will suffer root damage, and the beneficial soil microbes will die. 

Fluoride Levels

Houseplants usually take longer to react to fluoridated water because fluoride buildup in the soil and leaves is slow. However, when fluoride toxicity starts affecting photosynthesis and respiration, you’ll notice spots on the leaves

Unfortunately, this toxicity is irreversible. When you notice changes in the leaves, you have no option but to discard the affected plants. 

If the tap water contains fluoride, you are better off protecting your plants using a reverse osmosis filter.

pH Level

Plants prefer slightly acidic water because soil nutrients are more accessible. Soft water is slightly acidic and best for plants. On the other hand, hard water contains minerals, so it is alkaline. This is why rainwater is better than tap water

Fortunately, you can lower water pH using citric, nitric, and phosphoric acids. Adding reverse osmosis water and rainwater to tap water will also make it less alkaline.

Heavy Metals

Tap water and well water usually have heavy metals. They include copper, calcium, manganese, lead, and arsenic. These metals lower the quality of water. This is one of the reasons rainwater and distilled bottled water are of better quality, and tap water is of poor quality. 

These metals slow plant metabolism and growth. They also kill beneficial microbes in the soil. The best way to remove heavy metal from water is through reverse osmosis. 

Salinity Levels

Salinity rises when chlorine is added to water or when you use water softeners. High saline levels are bad for plants because the water displaces important nutrients, like potassium and phosphate, in the soil. It also interferes with nitrogen uptake.

The result is stunted growth, browning leaf tips, stem dieback, and dead root tips. 

Types of Water Best for Plant Growth

Choosing water for plants sometimes feels like a fight to find a balance. Some of the best water options are not always available or are costly. Sometimes, what is available may work, but you miss out on the plant’s potential because of the water quality. 

1. Rainwater

If you put a bucket or two outdoors, rainwater should be your first choice. When you observe your plants in the garden, they usually flourish during the rainy season. Your indoor plants will also thrive when you use rainwater.

Rainwater is great for several reasons:

  • It is 100% soft water. 
  • It is acidic, with a pH of 6.2 – 6.8.  
  • It contains macronutrients, such as nitrates. Plants absorb these nutrients faster, resulting in faster plant growth. 
  • It is rich in oxygen. Rainwater increases dissolved oxygen in the soil, leading to healthier roots and better nutrient absorption for the plant. 

Rainwater is best for plants when it is freshly collected. Unfortunately, rainwater gets contaminated easily, and it is not as beneficial to plants in this state. The solution is to store rainwater in a dark, tightly sealed barrel. 

2. Distilled Water 

Bottled distilled water is ideal for houseplants because it is available all year, unlike rain. So, after rainwater, the next best bet is distilled water.

Distilled water is better for houseplants because it is void of contaminants and other chemicals. It lacks minerals and hard metals, making it generally safer for plants and limiting mineral buildup in the soil. Microbial activities also remain uninterrupted when you use distilled water.

Unfortunately, distilled water has its limitations.

It is harder to obtain and is costly. The water also lacks essential minerals, such as calcium, magnesium, and potassium. Calcium helps with cell formation, magnesium makes it easier for plants to access soil nutrients, and potassium aids with root growth. 

That’s why I recommend switching to filtered or tap water occasionally.

However, remember to use distilled water every time you fertilize your houseplants. This way, water can dilute the fertilizer concentration or facilitate faster nutrient breakdown and absorption into plant root cells and prevent fertilizer burn.

Here is a video analyzing the different types of water, including distilled water, and their effect on plants: 

3. Filtered Water 

One of the best ways to handle tap water is to filter it before watering plants. The filtration system will remove chemicals and other impurities in the water.

The result? Plants get healthier water, making it easier for them to thrive.

Unfortunately, the water quality will depend on the filter you use. A reverse osmosis filter should be your first choice because it eliminates all minerals in the water. The water quality is consistent, the soil is safe from salt buildup, and the soil microbes are also preserved. 

Carbon filters eliminate chemicals like chlorine and chloramine but leave behind heavy metals and minerals. On the other hand, ion filters, replace mineral and heavy metal ions with sodium ions. These filters get rid of chemicals in the water, but the minerals and heavy metals left behind increase soil salinity. 

Unfortunately, the reverse osmosis water is also too pure. In the short term, RO water will flush out salts from the soil, and the plants will love it. However, plant growth will slow over time because plants also need minerals, albeit in small doses. 

The solution is to find a balance. Occasionally use tap water to introduce minerals into the soil, and then flush out the salts with RO water.

4. Tap Water

Tap water is one of the most controversial, with some people claiming it is okay for use on houseplants and others considering it harmful. Both claims are true because tap water quality varies depending on its source, chemicals used, and toxicity levels. 

However, even if your tap water is of better quality (lower chlorine and mineral level), it is not the best for plants, at least when compared to rain, distilled, and filtered water.  

Several tests have been carried out to check the effect of chlorinated water on microbial activity in the soil. One study used water with five parts per million (ppm) chlorine, and another contained 100 ppm of chlorine on plants. 

Both tests showed microbial activity in the soil slowed after plants were watered with chlorinated water. However, the effect was more adverse when water with a higher chlorine concentration was used. 

Fortunately, the bacteria in the soil multiplied quickly to the levels before tap water was used. There is just one problem. The regular disruption of microbial activity every single time you water your plants will ultimately slow plant growth. 

So, unless you take measures to improve the quality of tap water, it is best to stay away from it. Alternatively, you can swap tap water with rainwater or distilled water every other week. 

How to Make Faucet Water Safe For Plants

As discussed above, there are better options than tap water. However, if you have no choice but to use tap water, you should make it safer for your plants before using it.

Here’s how to do it. 

  • Let the water sit overnight. Collect the water in open containers and allow them to sit overnight. Chlorine evaporates within 24 hours. 
  • Distill the tap water. Distill the water to remove chlorine and other minerals.
  • Boil and cool the water. Boiling is a safer way of softening hard water than using water softeners. These softeners increase water salinity and salt buildup in the soil. 
  • Use water filters. Install water filters, preferably reverse osmosis filters. Carbon filters are also helpful in significantly reducing chloramine levels.

Except for distillation and filtration, these measures temporarily make tap water safe. Heavy metals and minerals remain in the water, even when chlorine and other chemicals are eliminated. 

In the short term, these minerals may not damage the soil. The plants will even utilize some. However, as the concentration builds up, the soil will become toxic.

Letting the tap water sit overnight allows the minerals to settle at the bottom of the container. To reduce the risk of introducing unwanted minerals into your potting mix, use only the upper half or 2/3 of the water.

Do Plants Grow Better With Tap Water or Distilled Water?

Plants need water to grow, but the type of water you use will determine how fast the plant grows. In some cases, the water slows or even halts the growth. Tap water and distilled water have different effects on plant growth.

Distilled water helps plants grow better because it is soft, has a neutral pH, and is free of minerals and contaminants. Plants easily access nutrients through distilled water. On the other hand, tap water has beneficial minerals. However, it also has contaminants that interfere with plant growth. 

Undoubtedly, distilled water is more beneficial and least likely to build toxicity in plants. It is a better choice, even with its drawbacks, which include high cost, inaccessibility, and absence of important nutrients.

Can You Use Hard Water on Houseplants?

Some hard water sources include tap, borehole, well, and river water. They contain high mineral concentrations, specifically calcium and magnesium, which harm plants and microorganisms in the soil. Despite all the doom and gloom, can you use it on houseplants?

You cannot use hard water on houseplants because it slows their growth and increases salt buildup in the soil. An increase in salt levels in the soil, in turn, reduces microbial activity. Over time, your plants will wilt, the leaves will turn brown, and the growth will be stunted.  

If your only choice is hard water, you can filter or boil it. These measures make hard water somewhat safer for plants. However, it is difficult to eliminate all harmful contaminants. If you can avoid it, staying away from hard water is best.

Can You Use Soft Water on Houseplants?

Soft water has low mineral concentrations. Rainwater, distilled water, and reverse osmosis water are examples of soft water. Filtered water can also be soft water, depending on the type of filter you use and the minerals removed from the water. 

You can use soft water on plants, as long as it is naturally soft, like rainwater or water whose minerals are filtered. However, avoid reliance on soft water because it lacks essential minerals. You should also avoid water softened with sodium chloride because it causes salt buildup in the soil.

Soft water is better for plants because they access water and nutrients easily. Some soft water sources, like rainwater, are better than others because they contain trace minerals important to plants. Some alternatives, like distilled and RO water, contain no minerals, so you shouldn’t be too dependent on them.

Conclusion 

The water you use on your plants is more or less about finding a balance. You need to look at the water quality, its effect on the soil, and how well the plant responds to the water. All these factors are interlinked. 

You may sometimes be forced to tap water because it is available, and the plants need the minerals. However, the cost will be salt buildup in the soil. 

The best way to handle the downsides of the water options available is to occasionally switch from one to the other, so the good in one source counters the bad in the other.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

Recent Posts