5-Minute Crafts
5-Minute Crafts

What Water to Use for a Fish Tank

Picture this: you bring aquarium fish in a plastic bag with water home, and there is a beautiful tank and a jar of fish food standing on the shelf. The only thing you need to do is fill the tank with water, but it’s very important to know what water you’re going to use.

At 5-Minute Crafts, we decided to find out what water is best for a fish tank.

Municipal tap water

This is probably the first option that comes to mind. After all, tap water is more accessible than any other water — it’s always at hand, and since people use it, it can be used for a fish tank, right? However, if you use tap water, you should know its composition because it varies from region to region. For example, water can be high in iron, magnesium, or even asbestos, which can be harmful for fish.

Additionally, tap water is usually disinfected with chlorine so that it can be consumed by people without being harmful, but chlorinated water can lead to fish illness. Aside from that, chlorine can disrupt the biological water filtration system in your tank and destroy beneficial bacteria. Therefore, if you choose to use tap water, it’s important to purchase a special water conditioner and dechlorinator. Or, if this is not possible, it’s necessary to let the water sit for several days before adding it to the tank.

Well water

Unlike tap water, it’s difficult to find out the composition of well water because no one tests it. Its properties and composition also vary and depend on the region where you live. For example, if you live in a place where agriculture is developed, then when it rains, fertilizers from the fields can enter the groundwater and saturate it with phosphates and nitrates, which is detrimental to fish. In some places, the water is very hard, and in others, it’s too soft. In short, this is not the best choice for a fish tank unless you are ready to check the composition of the water from time to time and adjust it yourself.

Bottled water

This may seem like an ideal solution for your fish tank — after all, bottled water is marketed as healthy, which means it’s good for fish. But it’s not that simple. Bottled water is often either well water, filtered water, or spring water that may contain a large amount of chlorine and minerals that are harmful to fish. Besides, this water is more expensive than those mentioned above, and if you have a large fish tank, this is an additional waste of plastic.


The obvious plus of this choice is that rainwater is absolutely free, but that’s probably it. This water can have unpredictable pH levels and contain air pollutants and asbestos from roof tiles if collected there. Therefore, you will have to purify this water and saturate it with necessary substances yourself.

River water

Some people think that river water would be ideal for a fish tank, as it’s the natural habitat of fish. However, it’s important to remember that water from a river or lake contains many different bacteria and parasites to which river fish have adapted but not aquarium fish. Typically, fish bred in captivity have a weaker immune system and are more susceptible to various pollutants. If you want to use river water for your fish tank, it must be disinfected.

Reverse osmosis water

If you have this system at home, congratulations, this water is almost ideal for a fish tank! It’s enough to add a remineralizer to it. Reverse osmosis is very effective because it has a fine membrane that only pure water can pass through, leaving any pollution and bacteria behind. However, the system will also filter out useful elements fish need, but this can be easily solved by adding a remineralizer and essential elements.

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