I am wondering if it is required to purify distilled water when changing the water in my betta fishes tank? or is that only necessary when using tap water?

thank you for taking the time to read and reply to my question


2 Answers 2


Distillation is a purification process by definition, so no, you don't need to purify it. What you do need to do is add back into distilled water some of what was removed by distillation if it is the only source of water in your tank. There are supplements for this purpose, a good store with solid fish knowledge can help you there, but I don't think it's really a good idea to go with just distilled water.

It's really probably better to look at distilled water for the purpose of tank top-up as a result of evaporation. The evaporated water is pure (this is actually how distillation works) and so the original mineral contents of the water remain behind. What that means is that adding in distilled water will maintain a consistent mineral content because the distilled water is not increasing it. Just give it a few hours exposed to pick up some additional oxygen or aerate it at bit, it will be lacking there.


You may have to purify it if was contaminated after distillation. If you believe that it hasn't had a chance to contaminate from particles in the air settling in it, things being dropped in it, animals drinking from it, or anything else you'd consider contamination, then you wouldn't because distillation removes everything that is not water.

However, distilled water is not good for a fish tank, because when you remove everything from the water, you remove things that people ( and most likely fish) need. I read somewhere ("Savage Garden" by Peter D'Amanto, I believe) that distilled water can actually pull certain nutrients out of you, instead of putting them into you. Certain amount of minerals and the like are good for you and would be for the fish as well. I'd stick to purified or treated water.

  • In short, it screws up your (or your animals') mineral household. That's also the reason why you shouldn't drink greater amounts of distilled water (takes minerals from your body) or saltwater (takes water from your body). It will always try to balance out the liquid/mineral ratio, but the minerals will never move. This is also the reason why doctors use saline solution rather than distilled water.
    – Mario
    Feb 28, 2015 at 11:05
  • @Mario Thanks for clarifying that. That's actually what I was trying to get across, but I couldn't remember exactly how the reasoning went. I think it did talk about the minerals and how drinking it can cause a person problems like you suggested.
    – Dalton
    Mar 2, 2015 at 18:16

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