rainwater safe?

[mooman]

I've seen numerous posts about using rainwater to keep the softwater loving apistos. I asked an employee at a lfs about using it instead of the r/o water I get from them. This store specializes in fish and generally has very knowledgeable employees. He said I would need to filter a 5g bucket of rainwater through carbon for several days and change the carbon at least once during that time in order to make it safe. This would of course negate any financial benefit I hoped to get by using rainwater. Is this guy just trying to sell me copious amounts of activated carbon, or is this common practice when using rainwater. I know "acid rain" is regional, but I'm not sure is it is a problem where I live (Columbus, OH). If we do have acid rain here, is it even detrimental, after all we're talking about fish that like it in the 5's right?

 

[Mike Wise]

You might find this strange but rainwater, even from the most clean areas of the world, runs around pH 5.5-5.8. This is due to CO2 that is dissolved into the raindrops as they fall. Once it touches the ground, chemicals in the soil buffer it to a usually higher neutral or alkaline pH.

Rainwater can be used if you collect it from areas where industrial & highway pollution are minor. Just remember not to collect water until about 15 minutes after it starts raining. This clears most of the pollutants out of the air & off the collecting surface (usually a roof with gutters & downspouts). Then it needs to be aerated & it certainly helps to run it through some high quality activated carbon (cheap glossy 'aquarium charcoal' is junk & not worth buying for any purpose except, maybe, starting charcoal fires without lighter fluid

) for about an hour/gallon. If you live in an area that gets a lot of rain, adding some 55 gallon plastic drums to the downspouts is worth the effort. Just remember to keep the covered so that dirt & mosquitos don't find a way in.

I don't do this because rainfall is rare in Denver.

 

[tjudy]

The surface you are collecting the water from is important. Aged roof shingles usually do not add contaminants, but new roof shingles probably add some petroleum byproducts. I would not collect off of a copper roof. The tile roofs that are popular in the west are pretty inocuous. I am not sure about propanel, but I suspect that it is ok.. so long as it is not copper. Wood shingles (usually redwood or cedar) are probably OK is they are well aged. Newer wood will likely leach contaminants.

I used to use rainwater in Indiana, but I collected water off an aged asphalt shingle roof, ran it through a 5-gallon bucket of loose-packed filter floss to catch junk, and then filtered with quality carbon for a few days. I gave it all up once I discovered RO/DI.