Water profile of rain water?

[Sadu]

I'll be housesitting for a few months shortly and might do some brewing there. The house collects rain water from the roof and stores it in a big concrete tank.

Given that we don't have a ward labs or similar in my country and getting a proper report is going to be too expensive to justify for a couple of brews - is there some baseline assumptions that can be made about rain water?

Similar to RO water or does it pick up different minerals depending which part of the sky it falls from? The water tastes excellent and seems soft, ie no calcium deposits on the shower etc.

Thanks in advance

(Also RO water isn't available either so that option is out).

 

[Miraculix]

It should be, theoretically, close to ro water, depending on what it pics up on the roof and in the air. I would worry about heavy metals or other nasty things that can be in the dust in the air and on the roof, don't know if it would be such a good idea to brew with it.

 

[ajdelange]

My tree hugger neighbor collects it and drinks it as do the residents of many places like the Virgin Islands, for example, and, presumably your country. I did a quicky analysis for my neighbor and found, as you would expect, a little chloride and a little sulfate. Don't remember how much exactly by a couple of mg/L. You can also expect nitrate, of course, from NOx emissions. The pH gives an indication of the total acid ions which can be present and, of course, it is a simple matter to get a TDS estimate from a conductivity meter. The content will vary quite a bit depending on what type of roofing you have. Shingles dissolve more stuff into collected rain water than metal does.

Heavy metals are not generally a concern with collected rain water. Tested samples of rain water generally meet WHO standards in this regard with the exception of Mn and Zn which, as their limits are based on aesthetics rather than health concerns, should not worry you unless the water tastes metallic. Zinc is good for yeast. Manganese is not. Where your concerns should be focused is on biological contamination. Many rainwater collection systems have filter beds, UV treatment lamps etc. to combat these. I ask my neighbor if he isn't more concerned about birds pooping on his collection surface than sulfuric acid but his only concern is that it is good for the environment. He has a perfectly good well (which, of course, delivers rain water). Why that isn't good enough for the environment I don't know. Perhaps the electricity needed to run the pump. But the electricity is generated from hydro where he lives. Nobody ever said tree huggers were rational (even though this guy has a PHD).

In any case your threat is more microbial than metalurgical. We can always argue that the boiling process would kill any organisms in your rain water and that you are quite safe on that basis.

 

[Miraculix]

Don't you think they there might be some heavy metals getting dissolved from the roof, depending on the roof materials used? Or that certain industries or big motorways may increase the amount of contaminated dust in the area which will then end up in the rainwater?

Especially after dry periods when dust and contaminants accumulated on surfaces, the first flush is always heavily contaminated in drainage systems, I was guessing that this must also be true for rainwater collection systems.

 

[kh54s10]

Don't you think they there might be some heavy metals getting dissolved from the roof, depending on the roof materials used? Or that certain industries or big motorways may increase the amount of contaminated dust in the area which will then end up in the rainwater?

Especially after dry periods when dust and contaminants accumulated on surfaces, the first flush is always heavily contaminated in drainage systems, I was guessing that this must also be true for rainwater collection systems.

It is probably true. But in the Virgin Islands most homes are built around a cistern. All the water used in the houses are collected rain water. I lived there, the water was fine, I rented so I don't know if or how the water was filtered.

In many places in the world this would be far cleaner water than what is consumed every day.

 

[ajdelange]

Don't you think they there might be some heavy metals getting dissolved from the roof, depending on the roof materials used?

That certainly seems a reasonable concern but apparently, as testing shows, it doesn't happen or doesn't happen to the extent that WHO MCLs (or whatever the WHO calls them) are exceeded except in the aesthetic group of ions.

Or that certain industries or big motorways may increase the amount of contaminated dust in the area which will then end up in the rainwater?

Again, quite reasonable to hypothesize that this could be problematical but, again, testing indicates that it isn't. In general. There are doubtless exceptions (live next door to a lead smelter or mercury refining plant).

Especially after dry periods when dust and contaminants accumulated on surfaces, the first flush is always heavily contaminated in drainage systems, I was guessing that this must also be true for rainwater collection systems.

Doubtless true. In fact, IIRC, my neighbor's system has some mechanism that automatically dumps the first collections after a period of no rain. Don't remember how it works though. Maybe it will come back to me (it was a couple of years ago he gave me a 'tour' of the system and I'm lucky if I can remember what happened last week).

 

[ajdelange]

A little research shows that a 'first flush' device is nothing more than a tee with the rain water entering at the left and passing to the cistern to the right. When it starts to rain the water doesn't go to the cistern but instead falls into the vertical arm of the tee. The bottom of the tee is capped with a small hole drilled into the cap. Thus if the incoming rate of flow is sufficient the water level rises in the vertical arm. There is a ball in this arm that floats on the water and when the water level approaches the horizontal part of the tee the ball fits into a seat and seals off the vertical arm. Water then flows to the cistern, or most of it does. A little is lost through the orifice at the bottom of the down pipe. The volume to be discarded is equal to the volume of the down pipe which is sized according to the catchment area of the collecting surface and the number of mm rainfall you wish to discard.

 

[shoengine]

That is brilliant engineering.

 

[Miraculix]

A little research shows that a 'first flush' device is nothing more than a tee with the rain water entering at the left and passing to the cistern to the right. When it starts to rain the water doesn't go to the cistern but instead falls into the vertical arm of the tee. The bottom of the tee is capped with a small hole drilled into the cap. Thus if the incoming rate of flow is sufficient the water level rises in the vertical arm. There is a ball in this arm that floats on the water and when the water level approaches the horizontal part of the tee the ball fits into a seat and seals off the vertical arm. Water then flows to the cistern, or most of it does. A little is lost through the orifice at the bottom of the down pipe. The volume to be discarded is equal to the volume of the down pipe which is sized according to the catchment area of the collecting surface and the number of mm rainfall you wish to discard.

Sounds pretty simple but effective.

 

[Sadu]

All the water used in the houses are collected rain water. I lived there, the water was fine, I rented so I don't know if or how the water was filtered.

In many places in the world this would be far cleaner water than what is consumed every day.

I think this is probably the case here. It's a rural property, not much in the way of smog or pollution, no arsenic refinery next door. There are no pipes in the streets so it's not a matter of people being hippies, it's just how everyone gets their water in this area.

I agree about the main issue being microbial from bird poop and such. I grew up drinking this water without any ill effects, there's a filter installed now which may or may not take care of this stuff for drinking. For brewing the bugs die in the boil anyway and it will nice to not have to deal with Chlorine for a change.