Watering is a gardening task we often complete on auto-pilot. However, the quality and components of the water you use impact the health of your plants more than you may think. Depending on where you live, tap water can contain a number of components that negatively impact plant health over time.
It is recommended to boil tap water before watering plants because tap water can contain chlorine and fluoride, along with salts like calcium and magnesium, that can build up in soil and stunt root growth. Tap water can also kill essential soil microbes, decreasing overall soil health.
While you can use tap water to water your plants occasionally, it is best to treat it in some way first to keep your plants healthy. This article explores the effects of tap water on plants, the pros and cons of boiling water, and other ways to improve tap water for plants.
Effects of Using Municipal Water for Watering Plants
There are several reasons why unfiltered and untreated tap water is not recommended for watering plants.
These concerns are dependent on the quality of the tap water in your region, but generally, these are the concerns to look out for:
Chlorine is added to water to kill disease-causing microbes. However, it does not discriminate when it comes to bacteria.
Watering plants with chlorinated water can also kill all the necessary microbes in the soil. While plants need chlorine in small amounts, an excess of chlorine in the soil can also stunt root growth, thereby affecting overall plant growth.
Grass can hold up better against chlorine toxicity than other plants or trees, but the primary concern is the buildup of chlorine in the soil over time. You can learn more about this in my article about whether it is possible to overwater new turf: Is It Possible to Water New Turf Too Much?
Fluoride is commonly added to tap water, but many plants are sensitive to fluoride buildup. Symptoms of toxicity include ‘burnt’ leaf tips and edges.
All water, even rainwater, contains salts and minerals. But these salts can appear in a higher concentration in tap water, especially hard tap water. An increase in salinity can lead to dehydration and burning in your plants as they struggle to retain water and move nutrients around the plant.
Increase in Soil pH
As most tap water contains minerals like calcium, it tends to be more alkaline. Watering plants with tap water can increase the pH value of the soil over time, which can become a problem for plants that prefer acidic soils.
Plants vastly prefer rainwater to tap water. But if you have no way to collect rainwater or don’t have any on hand, you can treat your tap water to make it safer for use on plants. One of the easiest ways to treat water if you have a small garden is simply to boil the water first.
Boiling Tap Water for Plants: Pros and Cons
Boiling water is one way of treating tap water to make it safe enough to water your plants. However, as with anything in gardening, there are pros and cons to doing so:
Pros: Reduces Chlorine and Hardness Levels and Kills Bacteria
There are several advantages of boiling water for plants:
Boiling water helps remove a lot of the chlorine in tap water. Beyond a certain temperature, chlorine evaporates into the air, so heating your water is one of the simplest ways of removing chlorine. This won’t remove all the chlorine, but the concentration will be greatly reduced.
Reduces Water Hardness
Sedimentation of salts occurs on the heated surface of the pot you’re using to boil your tap water. Boiling is a quick way of reducing the salinity of your tap water without having to filter it.
Kills Harmful Bacteria
You can make most water safe for drinking by boiling it. Boiling water kills pathogens, viruses, and most disease-causing bacteria that can affect the health of your plants.
Cons: Low Volume and Ineffective Against Heavy Metals and Fluoride
While there are definite benefits to boiling tap water for watering plants, this method has its limitations.
Here are some cons of boiling water for plants:
Only Feasible for Small Amounts of Water
You can only boil as much water as the size of your pots and the time you have allows. Boiled tap water also needs to be cooled before use, so you’ll need to factor in that time. Boiling tap water is only feasible if you have a few houseplants, not if you want to water an entire garden.
Doesn’t Filter Heavy Metals
While boiling water is good for removing most impurities, it cannot filter out any metals. If you suspect your water is contaminated, use a filtration system such as carbon filtering to keep yourself and your plants safe from heavy metal poisoning.
May Increase Fluoride Concentration
Unlike chlorine, which evaporates easily, fluoride is unaffected by boiling water. In fact, boiling your tap water can increase the concentration of fluoride as some water evaporates, reducing the amount of water that dilutes the fluoride.
Other Ways to Improve Tap Water Before Watering Plants
Considering these cons, it’s clear that boiling tap water is not always sufficient, especially if you suspect high levels of fluoride or metals in your water. And even if your water is safe, boiling it can be cumbersome, depending on how many plants you have.
Luckily, there are other methods you can use to treat tap water so that it’s safe enough to water your plants. No single approach will eliminate all contaminants, but boiling your water along with other methods listed here can greatly improve water quality.
Let the Water Sit
If you prefer not to boil your water to remove chlorine, you can allow it to sit in the sun for about 24 hours. The chlorine will evaporate over time, but this will not filter out any metals or fluoride, so only use it for a less labor-intensive—not safer—alternative to boiling water.
However, make sure to use a glass container when exposing your tap water to the sun as plastic containers may leach harmful chemicals into the water at high temperatures or under UV rays.
To learn more about the process, you can read my article: How Long Should Water Sit Before Using It On Plants?
Use an Activated Carbon Filter
An activated carbon filter is one of the best ways to filter tap water and make it safe for everything from drinking to watering your plants. Activated charcoal absorbs chlorine, fluoride, and heavy metals from tap water.
You may still need to let your water sit to eliminate any harmful particles or salts as the carbon filter will let those pass through. But when it comes to chemical removal, carbon filters are ideal.
Apply a Membrane Filtration System
Membrane filtration systems use a form of reverse osmosis to strain particulate matter, metals, salts, and fluoride from your tap water and make it safe to drink and water plants. These are one of the most effective ways of treating tap water but will need replacing over time.
Distill the Water
If you only have a few plants, you may consider buying bottled distilled water to water your plants. However, although it is better than using tap water on chlorine or fluoride-stressed plants, it can be an expensive alternative.
Many households have invested in high-quality water purifiers or distillers to make tap water safe for drinking. You can also use the same water for your plants.
Distilled water is water that is purified of all impurities through the process of evaporation and condensation. It is safe for your plants, but plants need some trace amounts of minerals to grow, so it’s best to supplement with fertilizers if you plan to use distilled water long-term.
It’s best to boil tap water before watering plants to protect them from chlorine toxicity and kill potential pathogens. However, boiling tap water will not eliminate heavy metals or fluoride, so you should consider using additional treatments to make your water safe. You can use activated carbon filters or membrane filtration systems in addition to boiling your tap water for the best possible water quality.