Water Sources for a Fish Tank

9 Best Water Sources for a Fish Tank

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If you’re planning on purchasing a fish tank, you’ve likely already planned out the aquascape and chosen the fish species you want to keep. Hold on a minute, though! One of the most crucial questions you’ll need to ask yourself is: what kind of water should you use?

The type of water you provide for your fish may have quite an influence on their overall health and well-being, so it’s important to choose wisely. If you choose the appropriate source for the water that will be in your tank, your fish will flourish, but if you don’t, you may end up with unhealthy fish.

The following is a list of several types of water that are most frequently used in fish tanks:

  1. Tap Water
  2. Well Water
  3. Reverse Osmosis (RO)
  4. De-Ionized Water (DI)
  5. Water from Another Aquarium
  6. Softened Water
  7. Bottled Water
  8. Rainwater
  9. Spring Water

Read on to learn a bit more about each of these to determine which option is best for your tank.

9 of the Best Water Sources for a Fish Tank

1.   Tap Water

Using tap water for an aquarium is the option that is often the best choice for most fish keepers and, in most cases, is the most economical choice as well. Almost anybody who maintains an aquarium has access to running water, and most of the time, your fish will do just fine with that water.

However, you will need to find out if the water from your tap comes from a municipal/city water supply. If it does, you likely have chlorine-mixed water. In this case, you will need to use a chlorine remover (machine filter or chemicals) to make the tap water safe for your tank’s aquatic inhabitants.

2.   Well Water

In contrast to tap water, there is no chance of chlorine being present in well water. However, its utilization may give rise to further problems.

To begin with, well water is not subject to the regulations that apply to municipal water. Because of this, the water that comes from your well may have high quantities of a number of different toxins, depending on where you live.

Additionally, because of runoff from agricultural land, the water may be contaminated with bacteria and nitrates that come from fertilizer.

What is even more concerning is that some of the runoff that may make its way into a source of well water can be from an industrial facility that introduces volatile organic substances such as the chemicals found in insecticides, lubricants, coatings, and herbicides.

This water differs in its hardness and acidity, and as it contains very little oxygen, it will need to be aerated before putting your aquarium fish in it.

3.   Reverse Osmosis (RO)

Reverse osmosis is a process that is used to clean water. The reverse osmosis process may remove up to 98-99% of the solids that are dissolved in any water, making that water then become extraordinarily pure and devoid of hardness, chemicals such as chlorine, and various pollutants. However, in order to make water that has been processed with reverse osmosis optimal for your fish, it is recommended that you make some adjustments to it since it’s the process is rather ineffective against certain bacteria. One of the methods you can use to make water treated with this method become more suitable is using a remineralizer like this one to restore the mineral balance that will have been altered.

4.   Deionized Water (DI)

I know that many fish keepers use a deionization unit connected to their plumbing to gain pure water for their fish tanks. The principle of deionized water (DI) is quite complex. Simply speaking, a deionization unit contains filters filled with a chemical resin, and the resin attracts and traps contaminants and exchanges them for the ingredients needed to create pure water. Deionized water is an excellent option to consider if you want to ensure that the water in your aquarium is clear of mineral and chemical impurities. Deionization can also filter out some contaminants that even reverse osmosis devices cannot remove, too.

Just like reverse osmosis water, though, you will also need to remineralize deionized water before using it.

5.   Another Aquarium’s Water

There is also the potential of using water from another aquarium. This approach offers several benefits and potential issues when you’re building up a new tank, but it may sometimes be quite beneficial. Using water from another tank might put your fish in danger of contracting an illness or exposing them to chemicals if you are not familiar with the history of the tank or the actual water conditions within it. This is especially true of the water that comes from the tanks at pet stores, where there is a high turnover of fish that might potentially bring an illness into the water without the store’s personnel having the opportunity to detect any such conditions.

In addition, the benefits that this provides to the cycling process are not particularly significant. Because the potential advantages of this choice in water are relatively low, it is not suggested that you do this. The one exception to this rule is when a used tank needs to be relocated. In this case, removing as much water as possible from the relocated tank will significantly assist in restarting the biological filter, provided that the filter was alive and functioning before the relocation of the used tank.

If you are a seasoned aquarium keeper and know the water quality in your tanks well, this may be a safe and beneficial option for you. However, for new tank enthusiasts or those that have less experience, you should be sure to take the safest route possible when sourcing the water for your new aquarium.

6.   Bottled Water

Even though this water supply appears to be the best option for a fish tank, it actually is not. Bottled water is the only type of water that is manufactured to be safe for human consumption, so it’s been modified specifically to benefit humans without any concern for the water being used for pets or other animals.

As previously indicated regarding filtered and purified water, this water supply could be deficient in some of the necessary components that fish require, or it might include minerals that are harmful to fish.

Before using bottled water for your aquarium, you must test it and make any necessary adjustments to ensure its suitable for your fish. In addition, a portion of bottled water contains high amounts of chlorine, and this will need to be removed before use.

Because bottled water is marked up at a higher price, maintaining the water in your aquarium will be a considerable financial burden for you if you wanted to use this option. Filling a fish aquarium with water from a bottle is also just a very unrealistic option, particularly for larger fish tanks, because of the high number of bottles that would be required to adequately accomplish the task.

Putting Minerals Back Into Your Drinking Water

For those who are contemplating utilizing distilled water, you may be curious about the remineralization process. Keep in mind that this is also necessary for the production of reverse osmosis water and de-ionized water as well.

Simply adding some tap water to your freshwater aquarium will often be enough to restore the loss of minerals that occurred during the purification processes. There are also remineralizing products available for purchase, and all it takes is a few drops of them to be added to your fish tank. The salt mix that is used for saltwater tanks contributes both salt and ions to the tank’s water. Regardless of which type of tank you’re setting up, there are plenty of options for remineralization and resolving any over-purification issues.

7.   Softened Water

Many individuals are interested in utilizing water that has been softened by a water softener that’s been placed in their homes. Even though this shouldn’t be a problem, you should still verify with the maker that your softened water is also recommended for use in a home aquarium. This will ensure that the water is suitable for your aquarium or not.

8.   Rainwater

Can you use Rainwater in Fish Tank

Some fish enthusiasts are curious about the possibility of using rainwater in their aquariums. For those wondering if this is a possibility, the answer is “yes!” Rainwater can also serve as one of the best natural water sources for aquariums.  However, the pH of rainwater can be different all over the world, so it’s best that you test the rainwater before you add it to your tank.

Additionally, if you live in a big city or near factories, the rainwater in your area may bring pollutants present in the air along with probable contaminants from pipes, gutters, tubing, and rooftops, all of which could be hazardous for your fish.

9.   Spring Water

Spring water helps provide a source of humidity that is relatively constant, and it’s a great option for delivering nutrients and inorganic salts. However, if you use spring water in excessive amounts, the pH of the water in your fish tank may become unstable, which is hazardous for the fish in your tank. Fish are extremely sensitive to even the slightest changes in pH and are at risk of suffering severe damage or potentially even passing away as a result.

The composition of spring water can fluctuate as well, both in terms of the minerals it contains and the pH of the water, which again creates an unstable situation. Since everything depends on the location and the source of these fluids, the levels of trace minerals will also be somewhat variable.

Any kind of fish might become used to a slow shift in pH, but a more volatile change would be fatal to them. In the same way that plants do, fish can use the minerals that may be found in certain water types, so this makes keeping an eye on what they’re absorbing especially important.

Additionally, certain minerals will control and maintain a consistent pH level in the water where they are present. Magnesium, calcium, and iron are some minerals that may be found in common spring water areas. The presence of these minerals in any spring is essential to the overall health of the fish population.

As a result of fast and severe urbanization and land use changes, many spring waters—particularly those in industrialized nations—are being negatively impacted by ecological issues. These issues include a decreased water supply, springs running dry, pollution, and other similar issues.

Do not jump to the conclusion that spring water is very pristine and does not contain any traces of pollution, though. It is very possible for springs to appear perfectly clean while being tainted with a wide variety of chemicals, some of which come from adjacent factories and farms. In particular, the pesticides that come from farms will be lethal to your fish. There is a possibility that the water in which your fish are kept contains pathogens like bacteria and viruses that can harm them, too.

What are the Benefits of Testing the Water Source in Your Fish Tank?

It is essential that you do a water quality test on any source of water that you want to use to fill your aquarium before you actually use it. Keep in mind that the survival of the fish is directly correlated to the quality of the water.

It is highly recommended that you begin by conducting tests for ammonia, calcium, nitrates, and phosphorous levels. In addition to checking for GH and KH, you should also check the pH. The test findings will direct you to what steps you need to take to ensure that the water is suitable for your fish.

Is Cloudy Water Bad for Your Fish?

Cloudy aquarium water isn’t bad for fish, but it does indicate an imbalance and potential issues. When you notice that the water in your aquarium is cloudy, you first need to check the water quality by using an aquarium water test (with or without a water kit). Establish a reference point for your nutritional levels, and then respond appropriately.


If you live in a location where the quality of water is poor or the water quality parameters do not meet the preferences of your fish, you should by now have a good notion of the proper water source for your fish.

The greatest thing you can do is educate yourself as much as possible on the contents of your aquarium to create the best habitat possible for your fish.