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How Long Does It Take For Tap Water To Be Safe For Fish?

We see a huge number of people reaching out and asking how long it takes for tap water to be safe for fish to live in every single month and we can see why.

Tap water is a quick, easy, and cheap option with the water that most pet stores sell for fish being extremely over priced for what it actually is and the fact that tap water will ofter work fine for most fish species.

Due to so many people reaching out and asking how long you have to leave tap water before putting your fish in as well as tap water being such a popular water source for fish, we have decided to publish this dedicated article going over the subject.

Our hope is that we will be able to help our readers avoid making some very simple and easy to avoid mistakes that we see people make time and time again when it comes to keeping their pet fish in tap water.

The vast majority of people keep a huge range of different fish species in tanks that are sources from tap water and when done correctly, it really can be a quick and easy option to fill your tanks.

Thankfully, the majority of our readers will simply need to wait for the chlorine in the water to fade out without having to add any additional chemicals to the water to keep costs down.

Some regions do add additional chemicals to their drinking water supply though so you will have to check the additives to tap water in your local regions.

How Long Does It Take For Tap Water To Be Safe For Fish?

That majority of tap water will be fine to add fish to after letting it sit in the tank for around 24 hours.

This gives the chlorine in the water time to oxidize and leave the water making it safer for your pet fish.

Some people do try to leave their tap water sitting for at least 48 hours though, especially for more sensitive fish species who can be chlorine sensitive.

The majority of tap water supplies do have chlorine contained within it but some regions do have other chemicals in the water too for various reasons.

Most of these chemicals will also oxidize with the air once out of the tap and leave the water supply if left for around three days though and then the water will be safe for most fish species.

There are a very small number of locations, usually in parts of Africa and Asia that add chemicals to the water that will need a compound adding to the water to remove it.

As the vast majority of our readers are from North America or Europe, this is not an issue for them and simply leaving the water in the tank to sit prior to putting your fish in it will usually be enough.

Do You Have To Let Tap Water Sit Before Putting Your Fish In It?

Although some people do put their fish into tap water without letting it sit, this can cause a number of problems with the main one being due to the chlorine in the water.

Due to chlorine having such a fast oxidization time, letting your tap water sit for around 24 hours prior to putting your fish into it is usually the best course of action to take.

In addition to the problems fish can have with the various chemicals in tap water, there can also be problems with the temperature of tap water too.

If you live in a colder location and the ambient temperature of the tap water is cold but the fish you have are sitting in water that is room temperature, you can cause temperature shock by adding your fish directly to the water and potentially kill them.

This is why we always recommend that you let your water sit for at least a day for the temperature to normalise and most of the chemicals in it to oxidise out of the water.

The majority of fish will be fine in the water that the come with for that time frame but ideally, you can pour the tap water into your tank or aquarium a day or two before going out to purchase your fish to allow you to add your new fish directly to your tank.

Should You Add Anything To Tap Water Before Putting Your Fish In The Tank?

Some people do use a tap water conditioner on any tap water that they will be adding to their tanks and although this does have a number of advantages, it is not essential by any means.

You can usually leave the tap water to site for a day or two to have the chlorine oxidise out of it and then add your fish to the water with minimal potential problems.

That said, most water conditioning products are cheap, easy to use, and offer additional benefits when looking to keep your fish in tap water.

This is why they are so popular with so many people choosing to use them on any tap water that they add to their aquarium.

Water conditioning products can also be a good thing to have when it comes to water changes too. It allows you to change the water in your aquarium subbing old water out for new tap water much quicker.

Depending on the fish species and plants that you plan to keep, you may actually have to do water changes on a regular basis with a water conditioner helping to save you a surprising amount of time.

What Are The Potential Risks Of Tap Water For Fish?

Tap water can have a number of potential risks for fish when it first comes out of the tap ranging from chlorine and other chemicals to the temperature of the water.

The vast majority of these problems are solved by simply leaving the tap water in a container to age for around 24 hours as the chlorine will oxidize and the temperature will normalize.

With there often being so many hidden costs with keeping aquariums, this really is a little win that should be taken advantage of as tap water is so cheap and you simply have to leave it to age in before using it.

As we mentioned above, many people who keep fish tanks and aquariums will keep a water conditioner in their supplies but these are not essential and they tend to be very cheap anyway.

If you keep salt water aquariums then there are additional steps that you have to take but the majority of people who we see reaching out about using tap water for their fish tanks are beginners and keeping fresh water fish.

This is why we are only focusing on fresh water aquariums for this article as most people who keep salt water aquariums are more experienced and already know what to do.

How Can You Tell If Tap Water Is Safe For Fish?

Although you can get chemical detector strips that will tell you if there is still chlorine in the tap water in your tank, they tend to be expensive so most people just leave the tap water to sit for around 24 hours and then add their fish to it.

The costs are just too high to get confirmation on the chemicals in the tap water prior to adding your fish making it un-economial for most people.

When it comes to telling if the temperature of the tap water is safe for fish, most people will keep some form of thermometer in their fish keeping supplies but if you have fish that are kept at room temperature, you are usually able to just dip your finger in.

Although this will not give you the exact temperature of the water, it is usually close enough for most people.

We know that we keep saying it but this is why so many people just our their tap water, let it sit for a day or two, and then add their fish to it.

This simple process solves the majority of problems when it comes to using tap water with your fish but has been proven to work time and time again for decades.


That brings our article going over how long it takes for tap water to be safe for fish to live in to an end. We hope that we have been able to help you prepare your tap water ready for your fish and as we have said time and time again in the article, simply letting the tap water sit for a day or two before adding your fish will remove the vast majority of potential problems. Time and time again though, we see people putting their fish directly into tap water without letting it sit resulting in a number of different problems.