Why is the tea darker?

I drink green tea, boiled in water, nothing else added. For awhile now, I have been boiling it, allowing to cool, then pour into bottles and put in the refrigerator -- a refreshing cool drink -- it is summer here.

I had recently been using tap water, despite years of drinking only spring water or rain water. Then a few days ago, I decided to go back to using spring water -- no access to rainwater these days.

That is when I noticed something. I always boil the tea twice, allowing to stand for a short time between boils, to extract more from the tea leaves. I followed this exact same regimen with the spring water, and this is the result:


...the tea on the left is boiled in tap water, on the right in spring water, "Aussie Natural" brand.

So, I wondered, was the tap water causing more to be extracted from the tea leaves, or was there some kind of chemical reaction between the chemicals in the tap water and the tea leaves?

I conducted another experiment, boiled the tea in spring water three times, allowing to stand over an hour between boils, and this is the result:


...the bottle on the extreme right has been boiled three times in spring water. Darker, but still nowhere near the tap water.

So, I am left wondering. A bit of a google around did not really reveal why the tea boiled in tap water is darker.

I am using Nerada organic green tea:

http://www.neradatea.com.au/index.php?route=product/product&product_id=76

This is what Aussie Natural have to say about their spring water:
http://www.aussienatural.net.au/about-our-natural-spring-water-perth

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