Rain Water

[dvonjr]

I collect rain water in two 55gal drums and was wondering if I can use that instead of tap water to fill my aquariums?

[Yanni]

It really just depends. What fish do you have in your tanks? What are your tap water parameters? Rain water is naturally acidic water and has practically nothing in it. If you had hard water or fish that preferred hard water, I wouldn't use rain water. If your tap water is also soft water, then rain water should be fine although I would use it with some caution. 

[dvonjr]

I am in the process of setting up a 45gal tank and was wondering if I could use rain water instead of tap water. Tap water usually has chlorine and/or fluoride which would have to be treated to use in an aquarium.

[tonyjuliano]

Rain water will be infinitely better than anything coming through a pipe.  Just be aware that, depending on your needs, you might have to adjust pH, and will most likely need to "up" the mineral content..

[preswash]

Al, who was the owner of Rocky Mountain Discus for many years once told me that rain water will kill your fish. His exact words were "it will turn them into floaters". I will never forget it. I believe Al has since retired. He was in bad health and is no longer selling fish. Rain water does pick things up on its way from the sky to any container.... For example, if it hits the roof then into a gutter then into a container it could certainly be contaminated. I mean, most gutters are pretty nasty inside and roof surfaces and shingles contain all kinds of nastys. Even if the rain fell out of the sky right into your tank it could still be suspect. If your want pure water you are much better off with an RO filter in my opinion. 

[tonyjuliano]

4 hours ago, preswash said:

rain water will kill your fish

Well, I’m definitely going to call “BS” on that statement- with exceptions.

In the “wild”, all aquatic beings live in rain water.  In nature, rain is the “top off” system.

in an aquarium environment, straight unadulterated rain water can be used in exactly the same fashion, to top off - without concern, and would be superior to anything coming out of you average household tap.

To use it “straight” for a large water change, or to fill a tank would likely be disastrous, as pH and mineral content would be woefully inadequate.  The pH of rain water is around 5, in urban environments it be as low as 4 (due to acidification). Way too acidic!  And the lack of carbonate hardness would lead to wild pH swings.  What most don’t realize is that most aquarium fish can acclimate to pH levels far outside of what may be “preferred”, but will be grievously injured if the pH (whatever level it is) varies significantly.  Stable pH is MUCH more important than what some say is “proper”.

One would need to adjust pH and mineralization for use in that particular situation.  Not hard to do, and again would be superior to you average tap water.

This is the “problem” that “Al” was likely alluding to.

I use RODI water for topping off all my tanks, but if I had easy access to rainwater in sufficient quantity, I would gladly use that instead.

Edited May 7, 2021 by tonyjuliano

[HenryC]

6 hours ago, tonyjuliano said:

Well, I’m definitely going to call “BS” on that statement- with exceptions.

In the “wild”, all aquatic beings live in rain water.  In nature, rain is the “top off” system.

in an aquarium environment, straight unadulterated rain water can be used in exactly the same fashion, to top off - without concern, and would be superior to anything coming out of you average household tap.

To use it “straight” for a large water change, or to fill a tank would likely be disastrous, as pH and mineral content would be woefully inadequate.  The pH of rain water is around 5, in urban environments it be as low as 4 (due to acidification). Way too acidic!  And the lack of carbonate hardness would lead to wild pH swings.  What most don’t realize is that most aquarium fish can acclimate to pH levels far outside of what may be “preferred”, but will be grievously injured if the pH (whatever level it is) varies significantly.  Stable pH is MUCH more important than what some say is “proper”.

One would need to adjust pH and mineralization for use in that particular situation.  Not hard to do, and again would be superior to you average tap water.

This is the “problem” that “Al” was likely alluding to.

I use RODI water for topping off all my tanks, but if I had easy access to rainwater in sufficient quantity, I would gladly use that instead.

https://www.cdc.gov/healthywater/drinking/private/rainwater-collection.html#:~:text=Germs and other contaminants are found in rainwater.&text=Rainwater can carry bacteria%2C parasites,been linked to disease outbreaks.

According to the CDC it can also drag down pollutants suspended in the air. Wouldn't risk it tbh.

Edited May 7, 2021 by HenryC

[Andy's Fish Den]

It can certainly be used, with caution. I know of a couple people who import fish, mainly out of South America that use rainwater in their tanks and then slowly acclimate the fish to tap water. If I was going to do it, I would be careful how it is collected. I would make sure that the container I am collecting into is clean and fish safe, clean out gutters well before setting up everything. I have seen how one guy does it, he collects off his house, it has a newer metal roof, so no possible leeching of anything from asphalt shingles, and has several food grade 55 gallon drums all plumbed to the down spouts and when they get full, there is piping to divert to yard. I also would be a little leery if I lived in a larger city.

You can also check out on YouTube, Patrick Neary collects and uses rainwater for his systems. I came across his channel a year or so ago, and his fish room is quite interesting in how its run. 

Rain water for your aquariums / tanks - YouTube

[preswash]

In nature rain water in rivers is filtered by the earth. The amount of rain water that enters rivers and oceans directly from the sky is insignificant as compared to the amount that enters from other sources.

Al was leary due to collection methods not ph or mineral content.

Henry C your first comment is outside of the forum's protocol.

[preswash]

Did you ever notice the black streaks on the outside of white gutters? They are caused by rain.

[tonyjuliano]

42 minutes ago, preswash said:

In nature rain water in rivers is filtered by the earth. The amount of rain water that enters rivers and oceans directly from the sky is insignificant as compared to the amount that enters from other sources.

Al was leary due to collection methods not ph or mineral content.

Henry C your first comment is outside of the forum's protocol.

Yeah well...

I’m an engineer, I have my undergrad in mechanical engineering and a masters degree in wastewater management, so I may know a little bit about what I’m talking about.

And the statement about the amount of water entering the bio-system via rainfall being insignificant?  Frankly, that’s absurd.

The simple fact is this...

Approximately 90% of the water on this earth is replenished by rain falling directly on various bodies of water (the oceans, lakes, rivers and streams).  No more than 10% of total rainfall is deposited on land.

Edited May 7, 2021 by tonyjuliano