Can I Use Distilled Water for Fish Tank?

As aquarists, we often face many questions related to the type of water to use in fish tanks or aquariums. For example, distilled water is safe for drinking by humans with moderationIs Distilled Water Safe to Use in A Fish Tank

But, can I use distilled water for a fish tank?

The short answer is, Yes! and NO! Distilled water can safely top up your fish tank/ aquarium water and reduce its hardness.

But the distillation process removes minerals like calcium. Therefore, the distilled water won’t help buffer pH and water hardness. This may be fatal to fish. But, remineralizing the distilled water will make it safe for use in your fish tank.

So, is Distilled Water Safe for Fish Tanks?

First, distilled water has no impurities and gases, which means it’ll be safe for your fish, as far as you add the advised minerals such as calcium or iron. 

Distilled water has a pH of 7 and contains both hydrogen and oxygen molecules.

Don’t fill your aquarium or fish tanks with distilled water as the distillation process removes all the minerals that are helpful to aquatic life.

For example, distillation will remove calcium and iron – minerals that are greatly required by fish.

Also, fish have semi-permeable membranes and thus pure distilled water can cause trauma to them.

For instance, Betta fish will surely experience trauma if you place them in pure distilled water.

You can sometimes top up the fish tank with distilled water. However, when you need to use pure distilled water in the fish tank, you must add some mineral deposits to make the water safe for fish.

Can I use distilled water for betta fish?

Distilled water must not be used in water tanks or aquariums for betta fish before adding the necessary nutrient minerals and controlling the water pH.

However, if you have no other water, you can use distilled water after adding the necessary nutrients. Distilled water exposes your Betta fish to the risk of death and lethargy. 

How to Make Distilled Water Safe for Fish

Since distilled water is free from any chlorine and impurities, it stands a better chance of being the best water for your fish tank but only if the lost minerals are added back.

This process is what is called remineralization and is pretty simple. You can do it at home.

The mineral supplements are available in pet stores or online stores. You will need to regularly add mineral supplements to maintain the perfect environment for your fish.

Alternatives to Distilled Waters for Fish Tank

Let me start by saying the best water for your fish tank is clean and fresh water that is chlorine-free and filtered.

That said, below are alternatives to distilled water that are great for your fish tank as well:

1. Reverse Osmosis Water

You can use Reverse Osmosis Water although it is mostly recommended for intermediate and expert fish keepers and not beginners.

This is because when RO water is exposed to any chemical, it can suddenly change its pH thus compromising the water in the tank and the fish. It takes practice to learn how to balance pH or RO water.

2. Purified Water

You can use purified water provided you adapt it to the needs of the fish. Purified water is water that has gone through the purification process to remove impurities.

However, during the process minerals are equally lost. So you will still need to add back the lost minerals as well as buffer the pH to make the water safe for your fish.

3. Tap Water

You can also use tap water so long it is chlorine-free. If it is not, be sure to use a chlorine remover or a de-chlorinator to make the water safe for your fish.

Also before you start using tap water for your fish tank, test it for chemicals, pH, kH, gH, and nitrates.


Distilled water itself is not the best water for your fish tank but once it is remineralized then it becomes safe to use for your fish.

It actually becomes the safest to use since it is pure and has all the necessary minerals added.

Recent Posts