[Lardman]

Now I actually have some rain water I thought Id test its pH.

One of these tubes is tap water the other rain water. I've misplaced the colour chart  but Im pretty sure that the rainwater has a higher pH than the tap 

[JayG]

You really need to find the chart Lardman! 

I can't think of anything that normally dissolves in rainwater (CO2, oxides of sulphur and nitrogen) which would make it anything other than (slightly) acidic, unless it has been collected from an area containing free lime (new(ish) cement is a possibility.)

[Yabba]

Scroll down @link ph colour chart

„

[gillie]

Our 'rainwater' is highly alkaline, more so than our hard tap water.

We think the reason is because it is collected off our cement tiled roof.  The tiles are pretty old but it does not seem to make any difference.