Home » Aquarium Guides » Can You Use Distilled Water In A Fish Tank? (No, Read Why!)

Can You Use Distilled Water In A Fish Tank? (No, Read Why!)

As fish tank owners, we all want to offer the best for our fish. And as you know, distilled water is considered the purest water in this world. So, anyone would think that it would be best to use distilled water in a fish tank. Then the question begins. Can you actually use distilled water in a fish tank?

You can use it under certain circumstances and after certain fixes. Although you think distilled water is best for your fish, in reality, it is not. Fish require minerals to thrive, which distilled water lacks.

So how do we make distilled water suitable for fish? Let’s discuss this topic in this article.

Can You Use Distilled Water In A Fish Tank

What is distilled water?

Distilled water is boiling water to separate it from impurities, minerals, and chemicals. After that, the steam will be cooled into liquid form, which becomes purified distilled water.

The process of heating and cooling the steam is called distillation. By distilling water, it removes many impurities and chemicals. Minerals are left behind after distillation. After that, distilled water is bottled in containers.

Although distilled water removes the impurities, some may not. Some contaminants have a low boiling point than water, which causes them to evaporate with water steam. Then, that mineral will also be distilled.

So, as you see, some impurities are not separated from the steam, and they will be in your distilled water. This explains why distilled water is easy to get contaminated.

What are the uses of distilled water?

Distilled water is used for industrial purposes, such as car battery cells or food processing equipment cleaning.

And also for home use, like steam irons and humidifiers. Distilled water is also used in laboratories to prepare other chemicals.

The difference between tap water and distilled water

Water distillers produce only pure water, while tap water is a mix of many types of water. That’s why distilled water is more friendly for fish than tap water. Tap water contains some minerals like calcium and magnesium, which are suitable for humans but bad for fish.

Tap water also contains chlorine to kill bacteria in the pipe system, which is also bad for fish. Distilled water does not have harmful chemicals and minerals but contains only pure water.

Can you use distilled water in a fish tank?

The answer is no! You should never ever put pure distilled water inside your fish tank.

Distilled water doesn’t have minerals mixed in it. The minerals are so crucial for the health of your fish. But, although distilled water lacks minerals, it doesn’t mean you should stay away from using it altogether.

As you know, distilled water is extremely pure. It has the basic elements of the water you need, but just in a very small amount needed for your fish to survive. Distilled water actually contains oxygen which is good for fish.

So, distilled water is useful but just as an addition to another kind of regular tap or well water. And then, you should take extra care when using it. Ensure that the water chemistry is well balanced before adding it to your fish tank.

Water chemistry in freshwater tanks

Water chemistry is important for freshwater fish. The pH level should be between 6.5 to 7.5, the water hardness below 12 dGH, and the temperature between 20 and 28 degrees Celsius.

You can monitor these aquarium water parameters using a liquid test kit every week or two weeks. When your water chemistry goes out of balance, your fish will show signs of stress.

In order to reach these parameters, you should prepare your distilled water before adding it to your freshwater aquarium. And, of course, you need to add some minerals back to your distilled water.

Water chemistry in saltwater fish tanks

Saltwater tanks will be similar to freshwater tanks. But you should know that saltwater fish need more intense water chemistry than freshwater fish.

Ensure that the pH level is between 8.1 to 8.4, the water hardness below 10 dGH, and the temperature between 24 degrees Celsius to 26 degrees Celsius.

You must first prepare your distilled water before adding it to your fish tank to meet these standards. Since saltwater has more minerals than freshwater, you will have to mix more minerals back into your distilled water.

Can You Use Distilled Water In A Fish Tank

What are the problems of using distilled water in a fish tank?

As you know already, minerals are important for your fish to survive in their environment. Distilled water doesn’t have enough minerals to support healthy fish, so you should add minerals back to it before using.

The problem is that either tap or distilled water contains chlorine and bacteria, which are harmful to fish.

So, to prevent your fish from getting sick or dying because of contaminated water, you should use a filter system.

A good filter system will clean your fish tank water from harmful elements and bacteria. So, you should not use tap or distilled water without a filter system.

Will distilled water kill fish?

If you use distilled water alone in your fish tank, your fish will die quickly. As distilled water doesn’t have any minerals, it can absorb salt and minerals from any object, including fish. So, when you put fish into distilled water, the salt content in the fish’s body will diffuse into the water.

This will cause serious physiological problems or death to your fish. So, you should never put your fish into pure distilled water.

What are the benefits of using distilled water in a fish tank?

Although pure, distilled water has some beneficial elements for your fish. It contains oxygen which is good for fish.

And you can use distilled water as a supplement to other kinds of regular tap or well water to keep the water chemistry balanced.

But as I already said, you should use a filter system to take out harmful elements and bacteria from distilled water before adding it to your fish tank.

When can I use distilled water in a fish tank?

Distilled water can be used in your fish tank for the following purposes:

Top off the tank to recover evaporation water losses. 

Water evaporation is normal for any fish tank. So, when your tank loses some water due to evaporation, you have to refill the tank.

As evaporation doesn’t take the mineral away, the water mineral levels go up so that your fish may not be able to bear it.

To fix this high mineral problem, you can top off your tank with distilled water. Distilled water has zero minerals. So, this will protect your fish against the high mineral levels in the tank.

Water changes after remineralization

Distilled water is safe to use in fish tanks after demineralization. Actually, it is one of the best types of water to use in fish tanks only if you remineralize it.

So, after remineralizing your distilled water, you can use it to fill the tank or for weekly water changes.

Reduce the hardness of your tap water.

Tap water in some areas is hard, and most freshwater fish can not survive in hard water. Fortunately, you can change this hardness level with the help of distilled water.

You can use distilled water to dilute the tap water so that it becomes soft enough for your fish. We recommend you add distilled water at a smaller percentage of 50% or 60% and keep monitoring the hardness level of the tank.

If you find out that the water hardness has not been reduced enough, you can add more distilled water and continue monitoring if it gets soft enough for your fish.

Replace saltwater

If you use fresh tap water in your marine aquarium or fish tank, there’s a high chance that it has too much chlorine and chloramines.

This happens especially when you use water from your kitchen sink. To protect your fish against these chemicals, you can add distilled water to adjust the saltwater.

How can I use distilled water in a fish tank?

If you are using distilled water to fix the water chemistry in your fish tank, you can use it right away without mixing anything.

However, if you use distilled water to fill the tank or change the water, you have to remineralize it first.

How to remineralize distilled water for the fish tank?

There are several ways you can try to remineralize distilled water.

Mix Epsom salt, calcium chloride, and baking soda

One of the best cost-effective ways to remineralize distilled water is mixing Epsom salt, calcium chloride, and baking soda.

Epsom salt will raise the magnesium level in distilled water. Calcium chloride brings the necessary minerals to ensure proper osmotic balance in your fish tank. Baking soda will raise the pH level of distilled water to neutral to be suitable for your fish.

Add water conditioner, baking soda, and acid buffer

You can also remineralize your distilled water using a water conditioner, baking soda, and acid buffer.

You will need to buy some water conditioner that contains essential minerals to do that. Then, you have to add baking soda to raise the pH level, and finally, use an acid buffer to bring the pH level down to around 7.

Add Seachem Equilibrium

Seachem Equilibrium is a very effective remineralizer made for aquarium use. You can simply mix it with your distilled water to remineralize it.

Using a commercial remineralizer like Seachem Equilibrium is better because it contains recommended amount of minerals and has instructions for proper dosage.

Can You Use Distilled Water In A Fish Tank

Other water types suitable for fish tanks

If it is remineralized, distilled water is considered one of the best water types for fish tanks. However, buying distilled water is not a cost-effective way to maintain your fish tank.

You can try some other water types if you don’t want to go through the hassle of remineralizing distilled water. 

Reverse Osmosis water

RO or reverse osmosis is a type of water that has been purified to remove any minerals and chemicals, making it safe to use for fish tanks.

It is available in the market widely, but you have to make sure that it is pure enough. If you have a RO system in your house, it is very cost-effective to use that water. You just have to ensure that the chlorine and chloramine levels are at 0 ppm. 


Springwater is another option, but most well water contains too much magnesium and calcium which can affect the pH level of your tank.

If you have spring water and it does not contain chemicals, then you can try using it for fish tanks after you test the water and get rid of chlorine.

Springwater is usually very low in pH levels, so you have to add baking soda to adjust it. Springwater is a good option if you have a soft water fish that requires low pH levels.

Bottled water

If you don’t want to mess up with the complicated process of remineralizing distilled water, you can try bottled water. There are many options in your local store, but make sure it’s suitable for fish tanks.

Tap water

Tap water is the cheapest option, but it usually contains chlorine and other chemicals that may harm your fish. To remove the harmful chemicals in tap water, you can use a water conditioner to make it safe for fish tanks.

No matter what type of water you choose, always test the water first and ensure it is safe for fish tanks.


You can use distilled water in a fish tank if you remineralize it first. Otherwise, your fish will suffer from a lack of minerals. 

If you are not willing to go through the hassle of remineralizing distilled water, then you can buy RO water, spring water, and bottled water.

Whatever type of water you use for fish tanks, always test it first before adding your fish.

Credit to : Michael Langerman
Read Next : 
API General Cure ( Is This A Cure For Everything?)
Water Mites In Fish Tank | Are They Dangerous? ( Probably! )
DIY Aquarium Caves | Do Fish Need Caves? ( Answer Is Here! )

Sharing is caring!

About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.