Rain Water In Tanks

[petertr]

The average pH of rainwater in good conditions is around 5 .....not neutrral as above
BigC

Anyone know why that is?

Pure water should be pH 7 (by definition!).


I suppose rain water will have no buffering capacity, so even the slightest absorbed impurity will have a high effect. Even CO2 ?

 

[oakes]

The average pH of rainwater in good conditions is around 5 .....not neutrral as above
BigC

Anyone know why that is?

Pure water should be pH 7 (by definition!).


I suppose rain water will have no buffering capacity, so even the slightest absorbed impurity will have a high effect. Even CO2 ?

Yes, i believe BigC was correct in correcting me! Whilst pure water has a pH of 7, rainwater apparently absorbs CO2 in the atmosphere which lowers the pH. The rainwater in my collection tank is 7, so i had assumed it was 7 when it fell out of the sky! Apparently not, but i don't know what has raised it back up from stated pH of 5. I live in an area free of most pollutants, the roof is painted steel and the tank lined with an inert liner.