Can You Water Plants With Tap Water? (& Other Watering Tips)


There are lots of water sources to choose from, including well water, filtered water, rainfall, and tap water. However, they are not all created equal, and each one has its uses.

So, can you water plants with tap water?  You can water plants with tap water, and most of them will be fine.  However, certain plants with long and thin leaves are sensitive to fluoride in tap water.  If you add water softeners to your tap water, the salts can harm plants.  Tap water with a very high pH (7.5 to 8.0 or higher) may make certain nutrients unavailable to plants.

Of course, there are ways to avoid some of the problems that tap water can present for plants.  For example, you can use filters or avoid tap water altogether.

In this article, we’ll talk about the potential problems that tap water can cause for plants.  We’ll also look into ways to solve the problem, along with alternatives to tap water.

Let’s dive in.

Can You Water Plants With Tap Water?

You can water plants with tap water without too much worry.  Most tap water sources will not cause major problems for most plant species (especially in the short term).

tap water
Most tap water is ok for plants, but you might want to check the pH, calcium, and magnesium levels first.

However, there are some potential problems with tap water from some cities and towns.  For example:

  • Water pH – some tap water has a high pH, which can make nutrients unavailable to plants.
  • Hard Water – this water has lots of dissolved calcium and magnesium, which raises pH.  Too much of one can prevent plants from absorbing the other.
  • Treatment Chemicals – this often refers to fluoride and chlorine, which are added to tap water by municipalities to kill bacteria and improve dental health.

The only way to know for sure that you have one or more of these problems is to do water testing.  You can get a test done privately, or you can ask the city or town for a copy of the water report.

You can find drinking water data and reports (by state) on the U.S. EPA website.

How To Make Tap Water Safe For Plants

To make tap water safe for plants, it is necessary to address the 3 potential issues listed above: water pH, hard water, and treatment chemicals.

Let’s start with water pH.

Reducing Tap Water pH For Plants

Tap water often has a high pH when it comes from rocky areas with lots of limestone (calcium carbonate).  Calcium dissolved in water increases pH (the same goes for magnesium dissolved in water).

Adding tap water with high pH to soil will raise pH over time.  You can see how soil pH affects nutrient availability in this chart from Research Gate (in particular, iron and boron start to become less available as pH rises from 7 to 8).

Many fertilizers will lower pH when dissolved in water (that is, they will make the water more acidic).  This can counter the effect of calcium and magnesium in hard water.

You can either do a soil test yourself or send a sample to your local agricultural extension office for testing.  You can learn more about soil testing in my article here.

Addressing Hard Water Problems In Tap Water (Water Softeners)

Hard water can be bad for plants, and it can corrode metal pipes.  It can also leave white or gray deposits when heated.

A water softening filter can address these problems.  According to the Penn State University Extension, this filter works by replacing calcium and magnesium ions in hard water with sodium ions.

One disadvantage of water softening is that the water now contains sodium.  This salt can harm plants in high concentrations.

Remember: the more calcium and magnesium that is removed by water softening, the more sodium is added to water.

Addressing Treatment Chemicals In Tap Water

There are two main treatment chemicals added to tap water by cities and towns:

  • Sodium hypochlorite (a form of chlorine) – this is often added to tap water to eliminate bacteria to safe levels.  Chloramine (a derivative of ammonia) may also be used for this purpose.
  • Fluoride – this is often added to tap water to improve dental health.

Chlorine & Chloramine In Tap Water

According to the University of Minnesota Extension, most plants are not very sensitive to chlorine in its various forms.  In fact, even beneficial bacteria in soil will recover quickly from watering with tap water that contains chlorine.

According to the Colorado State University Extension, most tap water does not contain enough chlorine to kill soil bacteria any deeper than half an inch.  Even more impressive is that the soil bacteria population returned to pre-chlorine levels in 2 days.

Does Letting Tap Water Sit Remove Chlorine & Chloramine?

Letting tap water sit removes some chlorine – but probably not all of it.  Usually, it is recommended to let tap water sit out in an open container for 24 hours to allow some chlorine to evaporate out of the water and into the air.

water
Letting water sit out for a day or more can remove some of the chlorine (but not chloramine).

Letting water sit out will also allow it to approach room temperature.  This is helpful if the water is coming out of the tap very cold, which can delay seed germination or shock warm-weather plants.

On the other hand, Tap Score suggests that chloramine (an alternative to chlorine) cannot be removed from water by evaporation.  Instead, you will need to use active removal, like a catalytic carbon filter.

Does Letting Tap Water Sit Distill It?

Letting tap water sit does not distill it.  There will still be a number of dissolved solids in tap water after it sits out, including:

  • Calcium
  • Magnesium
  • Iron
  • Heavy Metals

However, you can buy distilled tap water or make your own.  CNET has an article here on how to make distilled water.

Fluoride In Tap Water

Some plants with long and thin leaves are sensitive to fluoride, including:

  • Spider plant
  • Easter lily
  • Dracaena
  • Peace lily
  • Parlor Palm
  • Prayer Plant
  • Freesia

After enough time and exposure to fluoride in water, the leaf tips of these plants will turn brown.

dracaena
Leaf tips of Dracaena (and other plants with long, thin leaves) will turn brown if there is too much fluoride in the water.

To remove fluoride, you have two options:

  • Flush the soil with rain water or bottled water.  (This will remove some of the fluoride and hopefully reduce it to acceptable levels.)
  • Install a reverse osmosis system (these systems can cost thousands of dollars).

According to WebMD, EPA guidelines state that tap water pH in the US can range from 6.5 to 8.5.

Water with a pH on the high end of this range this will cause problems for plants.  For example, a high pH it will limit the availability of iron and other nutrients.

You can read this article to see what iron deficiency in plants looks like, and this article to find some fertilizers that are high in iron.

Is Filtered Water Good For Plants?

Filtered water is good for plants because it contains fewer harmful contaminants than unfiltered water.  However, remember that filtering can also remove minerals that plants can use for growth.

There are some different methods for filtering water.  Two interesting ones are reverse osmosis and sand filters.

Reverse Osmosis Water Filter

Desalination plants use reverse osmosis, which moves water from an area of high concentration to an area of low concentration.  According to the CDC, reverse osmosis systems will remove common contaminants from water, including:

  • Protozoa
  • Bacteria
  • Viruses
  • Chemicals (such as sodium, chloride, copper, chromium, and lead)

Reverse osmosis can also reduce (but may not eliminate):

  • Arsenic
  • Fluoride
  • Radium
  • Sulfate
  • Calcium
  • Magnesium
  • Potassium
  • Nitrate
  • Phosphorus

Of course, some of these substances (such as nitrate) are helpful for plant growth.  So, you may just end up adding some of them back into the soil with a fertilizer.

Home Depot sells reverse osmosis systems that go under the sink, such as this 5-Stage one from Essence.

You can learn more about how reverse osmosis systems work from Fresh Water Systems.

Sand Based Water Filters

A sand filter moves water through sand to clean it.  The water molecules can move through the sand, but the large contaminant particles cannot.

According to the CDC, a slow sand filter is a sand filter that households can use to clean well water or tap water.  Slow sand filters can remove:

  • 99.98% of protozoa
  • 90% to 99% of bacteria
  • Some viruses

You can find sand filters that are used for pools and ponds, such as this Hayward Pro Series Sand filter from Doheny’s.  These filters will remove some of the contaminants from well water before you use it in your garden.

The Michigan State University suggests that soil will also work to filter out contaminants from water (although protozoa, bacteria, and viruses may remain).

Do Plants Grow Better With Tap Water Or Distilled Water?

If your tap water has a high pH (7.5 to 8.0 or higher), then you are probably better off using distilled water for plants.  As mentioned earlier, a high pH can prevent plants from absorbing certain nutrients (such as iron).

In theory, distilled water should have a pH of 7.0 (neutral), since there is nothing dissolved in it. However, carbon dioxide will dissolve into distilled water on contact.

This will create carbonic acid, which can lower the pH of distilled water to 5.8 within hours after distilling.

If your tap water has a lower pH (less than 7.5), it is probably fine to use it for watering plants.  After you mix in fertilizer, it will lower the pH of the tap water further.

The exception would be if there are any heavy metals or contaminants (protozoa, bacteria, or viruses) in the tap water.  This can happen due to failure at a water treatment plant or a damaged pipe.

In that case, you shouldn’t spray any part of the plant that you harvest (for example, the leaves on lettuce or spinach, or the fruit on tomatoes or peppers.) 

green lettuce
Don’t spray lettuce leaves with tap water that may be contaminated.

Do Plants Grow Better With Tap Water Or Bottled Water?

Bottled water still has some minerals in it (which improves flavor – you wouldn’t like distilled water!)  However, the mineral levels are not as high as hard water that has lots of calcium or magnesium dissolved in it.

water bottles
Bottled water has some minerals in it that can help plants to grow.

Tap water still has some minerals in it.  However, there is always the potential for high pH, hard water, and contaminants (as mentioned earlier).

For that reason, you are probably better off watering plants with bottled water if you can afford it.  Another option is to consider a water filtration system, which could end up saving you money in the long run.

Do Plants Grow Faster With Tap Water Or Salt Water?    

Most plants will grow better with tap water.  However, there are some exceptions.

For example, some plants can tolerate salt water, and some are even adapted to grow in it.  According to Clemson University, plants such as rosemary and Mexican sunflower will tolerate salt and can grow in coastal regions.

rosemary plant
Rosemary can tolerate some salt water and still grow.

If you are growing salt-tolerant plants or acid-loving plants and your tap water has a high pH, you might be better off using salty water (such as water that has been treated softened).

What Kind Of Water Should I Use To Water My Plants?

One of the most natural sources of water for gardening is rain water.  In addition to allowing the rain to fall where it may, you can catch rain water in a barrel for storage and later use.

water barrel
Use a barrel to capture rain to use for watering when the weather is dry.

Just be sure to avoid mosquito growth by covering the water barrel after a rain (remember to uncover it before rain to harvest the water).

Well water can also work for watering a garden.  However, some of the same contaminants that appear in tap water can also show up in well water.

You can learn more about using well water for plants in my article here.

Conclusion

Now you know about what potential problems tap water can have for plants.  You also know how to address these problems.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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